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