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‎README.md

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@@ -95,3 +95,11 @@ Algorithms, 4th edition textbook code (using c++)
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| [-](https://algs4.cs.princeton.edu/44sp/index.php#-) | [Arbitrage.cpp](ch4/49_Arbitrage/main.cpp) | arbitrage detection | [-](https://algs4.cs.princeton.edu/44sp/index.php#-) | [FloydWarshall.h](ch4/head/FloydWarshall.h) | all-pairs shortest paths (dense) |
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| [-](https://algs4.cs.princeton.edu/44sp/index.php#-) | [AdjMatrixEdgeWeightedDigraph.h](ch4/head/AdjMatrixEdgeWeightedDigraph.h) | edge-weighted graph (dense) | | | |
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## ch5. Strings
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| REF | PROGRAM | DESCRIPTION / C++DOC | REF | PROGRAM | DESCRIPTION / C++DOC |
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| :---------------------------------------------------------: | :----------------------------------------------------------: | :----------------------: | :---------------------------------------------------------: | :----------------------------------------------------------: | :------------------: |
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| [-](https://algs4.cs.princeton.edu/50strings/index.php#-) | [Alphabet.java](https://algs4.cs.princeton.edu/50strings/Alphabet.java.html) | alphabet | [-](https://algs4.cs.princeton.edu/50strings/index.php#-) | [Count.java](https://algs4.cs.princeton.edu/50strings/Count.java.html) | alphabet client |
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| [5.1](https://algs4.cs.princeton.edu/51radix/index.php#5.1) | [LSD.h](ch5/head/LSD.h) | LSD radix sort | [5.2](https://algs4.cs.princeton.edu/51radix/index.php#5.2) | [MSD.h](ch5/head/MSD.h) | MSD radix sort |
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| [-](https://algs4.cs.princeton.edu/51radix/index.php#-) | [InplaceMSD.h](ch5/head/InplaceMSD.h) | In-place MSD radix sort1 | | | |
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‎ch5/3_LSD/CMakeLists.txt

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cmake_minimum_required(VERSION 3.8)
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project(3_LSD)
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set(CMAKE_CXX_STANDARD 14)
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set(SOURCE_FILES main.cpp ../head/LSD.h ../head/MSD.h ../head/InplaceMSD.h)
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add_executable(3_LSD ${SOURCE_FILES})

‎ch5/3_LSD/main.cpp

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#include "../head/LSD.h"
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#include <iostream>
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#include <fstream>
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using namespace std;
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/**
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* Reads in a sequence of fixed-length strings from standard input;
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* LSD radix sorts them;
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* and prints them to standard output in ascending order.
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*
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* @param args the command-line arguments
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*/
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int main() {
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string file = "/home/ace/AceDev/C++/algorithm/ch5/data/words3.txt";
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fstream in(file);
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string tmp;
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vector<string> a;
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while (in >> tmp)
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a.push_back(tmp);
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int n = a.size();
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int w = a[0].length();
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// sort the strings
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LSD::sort(a, w);
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// print results
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for (int i = 0; i < n; ++i)
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cout << a[i] << endl;
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}

‎ch5/4_MSD/CMakeLists.txt

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cmake_minimum_required(VERSION 3.8)
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project(4_MSD)
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set(CMAKE_CXX_STANDARD 14)
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set(SOURCE_FILES main.cpp ../head/LSD.h ../head/MSD.h)
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add_executable(4_MSD ${SOURCE_FILES})

‎ch5/4_MSD/main.cpp

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#include "../head/MSD.h"
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#include <iostream>
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#include <fstream>
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using namespace std;
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/**
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* Reads in a sequence of extended ASCII strings from standard input;
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* MSD radix sorts them;
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* and prints them to standard output in ascending order.
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*
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* @param args the command-line arguments
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*/
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int main() {
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string file = "/home/ace/AceDev/C++/algorithm/ch5/data/shells.txt";
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fstream in(file);
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string tmp;
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vector<string> a;
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while (in >> tmp)
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a.push_back(tmp);
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int n = a.size();
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int w = a[0].length();
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// sort the strings
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MSD::sort(a);
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// print results
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for (int i = 0; i < n; ++i)
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cout << a[i] << endl;
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}

‎ch5/5_InplaceMSD/CMakeLists.txt

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cmake_minimum_required(VERSION 3.8)
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project(5_InplaceMSD)
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set(CMAKE_CXX_STANDARD 14)
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set(SOURCE_FILES main.cpp ../head/LSD.h ../head/MSD.h)
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add_executable(5_InplaceMSD ${SOURCE_FILES})

‎ch5/5_InplaceMSD/main.cpp

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#include "../head/InplaceMSD.h"
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#include <iostream>
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#include <fstream>
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using namespace std;
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/**
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* Reads in a sequence of extended ASCII strings from standard input;
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* in-place MSD radix sorts them;
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* and prints them to standard output in ascending order.
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*
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* @param args the command-line arguments
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*/
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int main() {
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string file = "/home/ace/AceDev/C++/algorithm/ch5/data/shells.txt";
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fstream in(file);
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string tmp;
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vector<string> a;
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while (in >> tmp)
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a.push_back(tmp);
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int n = a.size();
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int w = a[0].length();
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// sort the strings
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InplaceMSD::sort(a);
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// print results
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for (int i = 0; i < n; ++i)
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cout << a[i] << endl;
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}

‎ch5/CMakeLists.txt

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cmake_minimum_required(VERSION 3.8)
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project(ch5)
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set(CMAKE_CXX_STANDARD 14)
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include_directories(head)
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include_directories(data)
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add_subdirectory(3_LSD)
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add_subdirectory(4_MSD)
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add_subdirectory(5_InplaceMSD)
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‎ch5/data/shells.txt

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she sells seashells by the sea shore
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the shells she sells are surely seashells

‎ch5/data/words3.txt

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bed bug dad yes zoo
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now for tip ilk dim
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tag jot sob nob sky
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hut men egg few jay
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owl joy rap gig wee
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was wad fee tap tar
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dug jam all bad yet

‎ch5/head/InplaceMSD.h

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#ifndef CH5_INPLACEMSD_H
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#define CH5_INPLACEMSD_H
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#include <vector>
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#include <string>
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using std::vector;
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using std::string;
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/**
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* The {@code InplaceMSD} class provides static methods for sorting an
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* array of extended ASCII strings using in-place MSD radix sort.
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* <p>
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* For additional documentation,
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* see <a href="https://algs4.cs.princeton.edu/51radix">Section 5.1</a> of
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* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
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*
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* @author Ivan Pesin
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*/
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class InplaceMSD {
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public:
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InplaceMSD() = delete;
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/**
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* Rearranges the array of extended ASCII strings in ascending order.
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* This is an unstable sorting algorithm.
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*
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* @param a the array to be sorted
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*/
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static void sort(vector<string> &a) {
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int n = a.size();
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sort(a, 0, n - 1, 0);
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}
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private:
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// sort from a[lo] to a[hi], starting at the dth character
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static void sort(vector<string> &a, int lo, int hi, int d) {
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// cutoff to insertion sort for small subarrays
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if (hi <= lo + CUTOFF) {
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insertion(a, lo, hi, d);
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return;
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}
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// compute frequency counts
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vector<int> heads(R + 2);
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vector<int> tails(R + 1);
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for (int i = lo; i <= hi; i++) {
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int c = charAt(a[i], d);
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heads[c + 2]++;
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}
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// transform counts to indices
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heads[0] = lo;
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for (int r = 0; r < R + 1; r++) {
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heads[r + 1] += heads[r];
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tails[r] = heads[r + 1];
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}
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// sort by d-th character in-place
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for (int r = 0; r < R + 1; r++) {
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while (heads[r] < tails[r]) {
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int c = charAt(a[heads[r]], d);
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while (c + 1 != r) {
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swap(a[heads[r]], a[heads[c + 1]++]);
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c = charAt(a[heads[r]], d);
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}
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heads[r]++;
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}
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}
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// recursively sort for each character (excludes sentinel -1)
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for (int r = 0; r < R; r++)
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sort(a, tails[r], tails[r + 1] - 1, d + 1);
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}
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// insertion sort a[lo..hi], starting at dth character
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static void insertion(vector<string> &a, int lo, int hi, int d) {
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for (int i = lo; i <= hi; i++)
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for (int j = i; j > lo && less(a[j], a[j - 1], d); j--)
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swap(a[j], a[j - 1]);
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}
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// is v less than w, starting at character d
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static bool less(string v, string w, int d) {
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// assert v.substring(0, d).equals(w.substring(0, d));
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for (int i = d; i < std::min(v.length(), w.length()); i++) {
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if (v[i] < w[i]) return true;
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if (v[i] > w[i]) return false;
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}
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return v.length() < w.length();
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}
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// return dth character of s, -1 if d = length of string
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static int charAt(string s, int d) {
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if (d == s.length()) return -1;
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return s[d];
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}
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private:
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static int R; // extended ASCII alphabet size
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static int CUTOFF; // cutoff to insertion sort
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};
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int InplaceMSD::R = 256;
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int InplaceMSD::CUTOFF = 15;
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#endif //CH5_INPLACEMSD_H

‎ch5/head/LSD.h

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#ifndef CH5_LSD_H
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#define CH5_LSD_H
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#include <string>
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#include <vector>
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using std::string;
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using std::vector;
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/**
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* The {@code LSD} class provides static methods for sorting an
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* array of <em>w</em>-character strings or 32-bit integers using LSD radix sort.
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* <p>
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* For additional documentation,
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* see <a href="https://algs4.cs.princeton.edu/51radix">Section 5.1</a> of
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* <i>Algorithms, 4th Edition</i> by Robert Sedgewick and Kevin Wayne.
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*
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* @author Robert Sedgewick
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* @author Kevin Wayne
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*/
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class LSD {
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public:
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// do not instantiate
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LSD() = delete;
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/**
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* Rearranges the array of W-character strings in ascending order.
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*
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* @param a the array to be sorted
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* @param w the number of characters per string
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*/
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static void sort(vector<string> &a, int w) {
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int n = a.size();
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int R = 256; // extend ASCII alphabet size
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vector<string> aux(n);
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for (int d = w - 1; d >= 0; d--) {
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// sort by key-indexed counting on dth character
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// compute frequency counts
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vector<int> count(R + 1);
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for (int i = 0; i < n; i++)
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count[a[i][d] + 1]++;
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// compute cumulates
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for (int r = 0; r < R; r++)
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count[r + 1] += count[r];
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// move data
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for (int i = 0; i < n; i++)
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aux[count[a[i][d]]++] = a[i];
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// copy back
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for (int i = 0; i < n; i++)
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a[i] = aux[i];
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}
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}
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/**
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* Rearranges the array of 32-bit integers in ascending order.
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* This is about 2-3x faster than Arrays.sort().
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*
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* @param a the array to be sorted
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*/
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static void sort(vector<int> &a) {
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int BITS = 32; // each int is 32 bits
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int R = 1 << BITS_PER_BYTE; // each bytes is between 0 and 255
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int MASK = R - 1; // 0xFF
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int w = BITS / BITS_PER_BYTE; // each int is 4 bytes
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int n = a.size();
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vector<int> aux(n);
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for (int d = 0; d < w; d++) {
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// compute frequency counts
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vector<int> count(R+1);
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for (int i = 0; i < n; i++) {
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int c = (a[i] >> BITS_PER_BYTE * d) & MASK;
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count[c + 1]++;
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}
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// compute cumulates
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for (int r = 0; r < R; r++)
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count[r + 1] += count[r];
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// for most significant byte, 0x80-0xFF comes before 0x00-0x7F
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if (d == w - 1) {
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int shift1 = count[R] - count[R / 2];
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int shift2 = count[R / 2];
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for (int r = 0; r < R / 2; r++)
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count[r] += shift1;
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for (int r = R / 2; r < R; r++)
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count[r] -= shift2;
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}
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// move data
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for (int i = 0; i < n; i++) {
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int c = (a[i] >> BITS_PER_BYTE * d) & MASK;
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aux[count[c]++] = a[i];
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}
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// copy back
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for (int i = 0; i < n; i++)
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a[i] = aux[i];
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}
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}
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private:
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static int BITS_PER_BYTE;
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};
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int LSD::BITS_PER_BYTE = 8;
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#endif //CH5_LSD_H

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