370

Author: yubinbai

README.md

@@ -3,6 +3,7 @@ Leetcode solutions in C++, Java, Python
 
 |#|Title|Solution|Difficulty|
 |---|-----|--------|----------|
+|370|[Range Addition](./src/range_addition)|[C++](./src/range_addition)|Medium|
 |369|[Plus One Linked List](./src/plus_one_linked_list)|[C++](./src/plus_one_linked_list)|Medium|
 |368|[Largest divisible subset](./src/largest_divisible_subset)|[C++](./src/largest_divisible_subset)|Medium|
 |367|[Valid Perfect Square](./src/valid_perfect_square)|[C++](./src/valid_perfect_square)|Medium|

src/range_addition/Makefile

@@ -0,0 +1,6 @@
+all:
+	clang++ main.cpp -o main.o -std=c++11
+
+run:
+	clang++ main.cpp -o main.o -std=c++11
+	./main.o

src/range_addition/README.md

@@ -0,0 +1,37 @@
+Problem
+===
+
+Assume you have an array of length n initialized with all 0's and are given k update operations.
+Each operation is represented as a triplet: [startIndex, endIndex, inc] which increments each element of subarray A[startIndex ... endIndex] (startIndex and endIndex inclusive) with inc.
+Return the modified array after all k operations were executed.
+
+Example:
+
+    Given:
+    length = 5,
+    updates = [
+      [1,  3,  2],
+      [2,  4,  3],
+      [0,  2, -2]
+    ]
+                                    
+    Output: [-2, 0, 3, 5, 3]
+    
+Initial state:
+[ 0, 0, 0, 0, 0 ]
+
+After applying operation [1, 3, 2]:
+[ 0, 2, 2, 2, 0 ]
+
+After applying operation [2, 4, 3]:
+[ 0, 2, 5, 5, 3 ]
+
+After applying operation [0, 2, -2]:
+[-2, 0, 3, 5, 3 ]
+    
+Solution
+===
+- Similar to segment tree
+- View interval as two operations: one to increase [start, n), another to decrease [end+1, n)
+- Pre-process all segments before carrying out increments
+- Half-open, half-close intervals are easier to manage

src/range_addition/main.cpp

@@ -0,0 +1,46 @@
+#include <algorithm>
+#include <cstdlib>
+#include <iostream>
+#include <map>
+#include <queue>
+#include <set>
+#include <sstream>
+#include <stack>
+#include <string>
+#include <unordered_map>
+#include <unordered_set>
+#include <vector>
+
+using namespace std;
+
+class Solution {
+public:
+  vector<int> getModifiedArray(int length, vector<vector<int>> updates) {
+    vector<int> results(length);
+    for(auto update: updates) {
+      results[update[0]] += update[2];
+      if (update[1] + 1 < length) {
+        results[update[1] + 1] -= update[2];
+      }
+    }
+    int value = 0;
+    for(int i = 0; i < length; i++) {
+      value += results[i];
+      results[i] = value;
+    }
+    return results;
+  }
+};
+
+int main() {
+  Solution sol;
+  vector<vector<int>> updates = {
+    {1,  3,  2},
+    {2,  4,  3},
+    {0,  2, -2}
+  };
+  for (auto i : sol.getModifiedArray(5, updates)) {
+    cout << i << ' ';
+  }
+  return 0;
+}