LeetCode - Maximum Size Subarray Sum Equals k

MaximumSizeSubarraySumEqualsk.java

// Given an array nums and a target value k, find the maximum length of a subarray that sums to k. If there isn't one, return 0 instead.

// Example 1:
// Given nums = [1, -1, 5, -2, 3], k = 3,
// return 4. (because the subarray [1, -1, 5, -2] sums to 3 and is the longest)

// Example 2:
// Given nums = [-2, -1, 2, 1], k = 1,
// return 2. (because the subarray [-1, 2] sums to 1 and is the longest)

// Follow Up:
// Can you do it in O(n) time?

public int maxSubArrayLen(int[] nums, int k) {
    if(nums == null || nums.length == 0) return 0;
    int[] sums = new int[nums.length + 1];
    Map<Integer, Integer> map = new HashMap<>();
    // map.put(0, -1);
    for(int i = 0; i < nums.length; i++){
        sums[i+1] = sums[i] + nums[i];
        map.put(sums[i+1], i+1);
    }
    int max = Integer.MIN_VALUE;
    for(int i = 0; i < sums.length; i++){
        int val = k + sums[i];
        if(map.containsKey(val)){
            max = Math.max(max, map.get(val) - i);
        }
    }
    return max > 0 ? max : 0;
}