GFG PTOD | 15 Jan 2025 | Longest Subarray with Sum K

int longestSubarray(vector<int>& arr, int k) {
        // code here
        int presum = 0, res=0;
        unordered_map<int, int> mp;
        for(int i=0; i<arr.size(); i++) {
            presum += arr[i];
            if(presum == k)
                res = max(res, i+1);
            else if(mp.find(presum-k) != mp.end())
                res = max(res, i-mp[presum-k]);
            
            if(mp.find(presum) == mp.end())
                mp[presum] = i;
        }
        return res;
    }