added dsa essential code

Author: Prateek Narang

.DS_Store

@@ -0,0 +1,34 @@
+
+#include<iostream>
+using namespace std;
+
+
+int main(){
+
+	int marks[100] = {-1};
+
+	int n;
+	cout<<"Enter the no of students ";
+	cin>>n;
+
+
+	//Input
+	for(int i=1; i<=n; i++){
+		cin>> marks[i];
+
+		marks[i] = marks[i]*2;
+	}
+
+	//Update 
+
+
+	//Output
+	for(int i=0;i<100;i++){
+		cout<< marks[i] <<" ,";
+	}
+
+	cout <<endl;
+
+
+	return 0;
+}

02 Arrays/.DS_Store

@@ -0,0 +1,37 @@
+
+#include<iostream>
+using namespace std;
+
+void printArray(int * arr,int n){
+
+
+	cout <<"In Function "<<sizeof(arr) <<endl;
+	arr[0] = 100;
+	for(int i=0;i<n;i++){
+		cout << arr[i] <<endl; 
+	}
+
+}
+
+
+int main(){
+
+	int arr[] = {1,2,3,4,5,6};
+
+	int n = sizeof(arr)/sizeof(int);
+
+
+	
+	printArray(arr,n);
+
+	
+	cout <<"In Main "<<sizeof(arr) <<endl;
+	for(int i=0;i<n;i++){
+		cout << arr[i] <<endl; 
+	}
+
+	
+
+
+	return 0;
+}

02 Arrays/01array.cpp

@@ -0,0 +1,36 @@
+#include<iostream>
+using namespace std;
+	
+
+int linear_search(int arr[],int n,int key){
+
+	for(int i=0; i<n; i++){
+		//Check if current element matches with the key
+		if(arr[i] == key){
+			return i;
+		}
+	}
+	//out of the loop 
+	return -1;
+}
+
+
+int main(){
+
+	int arr[] = {10,15,12,9,6,4,3,10,8};
+	int n = sizeof(arr)/sizeof(int);
+
+	int key;
+	cin>>key;
+
+	int index = linear_search(arr,n,key);
+	if(index!=-1){
+		cout<<key <<" is present at index "<< index <<endl;
+	}
+	else{
+		cout<<key <<" is NOT Found!" <<endl;
+	}
+
+
+	return 0;
+}

02 Arrays/02array.cpp

@@ -0,0 +1,61 @@
+#include<iostream>
+using namespace std;
+
+//Problem : Print all subarrays of a given array
+// Brute Force Approach O(N^3)
+int largestSubarraySum1(int arr[],int n){
+
+	int largest_sum = 0;
+
+	for(int i=0;i<n;i++){
+		for(int j=i; j<n; j++){
+
+			int subarraySum = 0;
+
+			for(int k=i; k<=j; k++){
+				//cout<<arr[k] <<",";
+				subarraySum += arr[k];
+			}
+			//put a check is subarraySum > largest_sum
+			largest_sum = max(largest_sum,subarraySum);
+
+		}
+	}
+	return largest_sum;
+}
+// Prefix Sum Approach O(N^2)
+int largestSubarraySum2(int arr[],int n){
+
+	//Prefix Sums
+	int prefix[100] = {0};
+	prefix[0] = arr[0];
+	
+	for(int i=1;i<n;i++){
+		prefix[i] = prefix[i-1] + arr[i];
+	}
+
+	//largest sum login
+	int largest_sum = 0;
+
+	for(int i=0;i<n;i++){
+		for(int j=i; j<n; j++){
+			int subarraySum = i>0 ? prefix[j] - prefix[i-1] : prefix[j];
+			//put a check is subarraySum > largest_sum
+			largest_sum = max(largest_sum,subarraySum);
+
+		}
+	}
+	return largest_sum;
+}
+
+int main(){
+	//Array Containing 
+	int arr[] = {-2,3,4,-1,5,-12,6,1,3};
+	int n = sizeof(arr)/sizeof(int);
+
+	cout<< largestSubarraySum1(arr,n) <<endl;
+	cout<< largestSubarraySum2(arr,n) <<endl;
+
+
+	return 0;
+}

02 Arrays/03_linear_search.cpp

@@ -0,0 +1,47 @@
+#include<iostream>
+using namespace std;
+	
+
+int binary_search(int arr[],int n,int key){
+	//Implement binary search
+	int s = 0;
+	int e = n - 1;
+
+	while(s<=e){
+		int mid = (s+e)/2;
+
+		if(arr[mid] == key){
+			return mid;
+		}
+		else if(arr[mid] > key){
+			e = mid - 1;
+		}
+		else{
+
+			s = mid + 1;
+		}
+	}
+
+	return -1;
+}
+
+
+int main(){
+
+	int arr[] = {10,20,30,40,45,60,70,89};
+	int n = sizeof(arr)/sizeof(int);
+
+	int key;
+	cin>>key;
+
+	int index = binary_search(arr,n,key);
+	if(index!=-1){
+		cout<<key <<" is present at index "<< index <<endl;
+	}
+	else{
+		cout<<key <<" is NOT Found!" <<endl;
+	}
+
+
+	return 0;
+}

02 Arrays/Subarray_sum_1.cpp

@@ -0,0 +1,29 @@
+#include<iostream>
+using namespace std;
+
+int maximum_subarray_sum(int arr[],int n){
+
+	int cs = 0;
+	int largest = 0;
+
+	for(int i=0;i<n;i++){
+		cs = cs + arr[i];
+		if(cs < 0){
+			cs = 0;
+		}
+		largest = max(largest, cs);
+	}
+
+	return largest;
+}
+
+
+int main(){
+	//Array Containing 
+	int arr[] = {-2,3,4,-1,5,-12,6,1,3};
+	int n = sizeof(arr)/sizeof(int);
+
+	cout<< maximum_subarray_sum(arr,n) <<endl;
+
+	return 0;
+}

02 Arrays/binary_search.cpp

@@ -0,0 +1,32 @@
+#include<iostream>
+using namespace std;
+
+//Problem : Print all subarrays of a given array
+void printSubarrays(int arr[],int n){
+
+	for(int i=0;i<n;i++){
+		for(int j=i; j<n;j++){
+			for(int k=i;k<=j;k++){
+				cout<<arr[k] <<",";
+			}
+			cout <<endl;
+		}
+
+	}
+
+}
+
+// Print the sum of each subarray & find out the largest sum
+
+
+int main(){
+	//Array Containing 
+	int arr[] = {-2,3,4,5,-12,6,2,3};
+	int n = sizeof(arr)/sizeof(int);
+
+	printSubarrays(arr,n);
+
+
+
+	return 0;
+}

02 Arrays/kadanes_algorithm.cpp

@@ -0,0 +1,40 @@
+#include<iostream>
+using namespace std;
+
+//Problem : Reverse all the elements of a given array
+void reverseArray(int arr[],int n){
+
+	int s = 0;
+	int e = n - 1;
+
+	while(s < e){
+		swap(arr[s],arr[e]);
+		s += 1;
+		e -= 1;
+	}
+
+}
+
+
+int main(){
+
+	int arr[] = {10,20,30,45,60,80,90};
+	int n = sizeof(arr)/sizeof(int);
+
+	//Print the Output
+	for(int i=0; i<n; i++){
+		cout << arr[i] << " ";
+	}
+	cout <<endl;
+
+
+	reverseArray(arr,n);
+
+	//Print the Output
+	for(int i=0; i<n; i++){
+		cout << arr[i] << " ";
+	}
+	cout <<endl;
+
+	return 0;
+}

02 Arrays/print_all_pairs.cpp

@@ -0,0 +1,36 @@
+#include<iostream>
+#include<ctime>
+using namespace std;
+
+bool compare(int a,int b){
+	return a > b;
+}
+
+//Sort the elements in increasing order 
+void bubble_sort(int a[],int n){
+
+	for(int times=1;times<=n-1;times++){
+		//repeated swapping
+		for(int j=0; j <= n - times - 1; j++ ){
+			if(compare(a[j],a[j+1])){
+				swap(a[j],a[j+1]);
+			}
+		}
+
+	}
+}
+
+
+
+
+int main(){
+	int arr[] = {-2,3,4,-1,5,-12,6,1,3};
+	int n = sizeof(arr)/sizeof(int);
+	
+
+	bubble_sort(arr,n);
+
+	
+
+	return 0;
+}