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# Finding subarray with given sum

In the article, we are going to find a subarray which sums to an input sum. This problem came in coding round of Visa, Amazon.
Submitted by Radib Kar, on November 22, 2018

Problem Statement: Given an unsorted array A of size N of non-negative integers, find a continuous sub-array which adds to the given number.

Solution

Algorithm:

1. A in the input array, n is the length of the array & s in the given sum.
2. Initialize vector b. (for storing indexes of subarray)
3. Initialize a variable cur_sum=0
4. for i=0:n-1
5. ```	set cur_sum=A[i]
for j=i+1:n-1
add A[j] to cur_sum
if(cur_sum==s)
i is the starting index of subarray found
j is the end index of subarray found
print elements between indexes i & j
(including i & j) & return to main
end if
if cur_sum become greater than s then break loop
end for
end for
```
6. If control comes out of the loop that means so such subarray exists, thus print "no subarray found".

## C++ implementation to find subarray with given sum

```#include <bits/stdc++.h>
using namespace std;

vector<int> find(vector<int> a,int n,int s){
vector<int> b; //output vector
int cur_sum=0;
for(int i=0;i<n;i++){
cur_sum=a[i];//cur_suming element
for(int j=i+1;j<n;j++){
//add next element contigeously
cur_sum=cur_sum+a[j];
// if current sum  is eaqual to the sum value
if(cur_sum==s){
//insert array index of the cur_sum element in sub array
b.push_back(i);
//insert array index of the last element in sub array
b.push_back(j);
return b;
}
if(cur_sum>s)
break;
}
}
// if no such sub array exists
b.push_back(-1);
return b;
}

int main() {
//code
int s,n,no;
cout<<"enter array length & Sum respectively"<<endl;
scanf("%d%d",&n,&s);

vector<int> a; //input array

cout<<"enter array elements........"<<endl;
for(int j=0;j<n;j++){
scanf("%d",&no);
a.push_back(no); //inserting array elements
}

vector<int> b=find(a,n,s);
if(b[0]==-1)
printf("subarray not found");
else{
cout<<"Subarray is: ";
for(int i=b[0];i<=b[1];i++)
cout<<a[i]<<" ";
cout<<endl;
}
return 0;
}
```

Output

```First run:
enter array length & Sum respectively
8
20
enter array elements........
4
2
10
3
-3
10
5
5
Subarray is: 10 3 -3 10

Second run:
enter array length & Sum respectively
6
15
enter array elements........
5
1
-6
7
7
3
subarray not found
```
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