Given an array arr[] containing integers and an integer k, your task is to find the length of the longest subarray where the sum of its elements is equal to the given value k. If there is no subarray with sum equal to k, return 0.

def longestSubarray(self, arr, k):  
    curr = 0
    prefix = { 0 : -1 }
    ans = 0
    for i in range(len(arr)):
        curr += arr[i]
        if curr - k in prefix: # check if prefix available
            ans = max(ans, i - prefix[curr - k])
        if curr not in prefix:
            prefix[curr] = i  # store prefix
    return ans

This is based on prefix sum. One can represent a subarray as difference of 2 prefix subarrays. We store the prefix sum and check for it in the loop

Questions

1. https://practice.geeksforgeeks.org/problems/longest-sub-array-with-sum-k0809/1?utm_source=youtube&utm_medium=collab_striver_ytdescription&utm_campaign=longest-sub-array-with-sum-k