Maximum Size Subarray Sum Equals k in C++

Suppose we have an array called nums and a target value k, we have to find the maximum length of a subarray that sums to k. If there is not present any, return 0 instead.

So, if the input is like nums = [1, -1, 5, -2, 3], k = 3, then the output will be 4, as the subarray [1, - 1, 5, -2] sums to 3 and is the longest.

To solve this, we will follow these steps −

• ret := 0

• Define one map m

• n := size of nums

• temp := 0, m[0] := -1

• for initialize i := 0, when i < n, update (increase i by 1), do −

  • temp := temp + nums[i]

  • if (temp - k) is in m, then −

    • ret := maximum of ret and i - m[temp - k]

  • if temp is not in m, then −

    • m[temp] := i

• return ret

Example 

Let us see the following implementation to get better understanding −

 Live Demo

#include <bits/stdc++.h>
using namespace std;
class Solution {
public:
   int maxSubArrayLen(vector<int<& nums, int k) {
      int ret = 0;
      unordered_map <int, int> m;
      int n = nums.size();
      int temp = 0;
      m[0] = -1;
      for(int i = 0; i < n; i++){
         temp += nums[i];
         if(m.count(temp - k)){
            ret = max(ret, i - m[temp - k]);
         }
         if(!m.count(temp)){
            m[temp] = i;
         }
      }
      return ret;
   }
};
main(){
   Solution ob;
   vector<int< v = {1,-1,5,-2,3};
   cout << (ob.maxSubArrayLen(v, 3));
}

Input

[1,-1,5,-2,3], 3

Output

4