325. Maximum Size Subarray Sum Equals k

Maximum Size Subarray Sum Equals k

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.

Note:

The sum of the entire nums array is guaranteed to fit within the 32-bit signed integer range.

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?

Solution

public class Solution {
     public int maxSubArrayLen(int[] nums, int k) {
        Map<Integer, Integer> map = new HashMap<>();

        int sum = 0;
        int result = 0;
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];

            if (sum == k) result = Math.max(result, i+1);
            if (map.containsKey(sum - k)) {
                result = Math.max(result, i - map.get(sum - k));
            }

            if (!map.containsKey(sum)) {
                map.put(sum, i);
            }
        }

        return result;
    }
}