_325.java

package com.fishercoder.solutions;

import java.util.HashMap;
import java.util.Map;

/**
 * 325. 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?*/

public class _325 {

    public static class Solution1 {
        public int maxSubArrayLen(int[] nums, int k) {
            Map<Integer, Integer> map = new HashMap();
            int sum = 0;
            int max = 0;
            for (int i = 0; i < nums.length; i++) {
                sum += nums[i];
                if (sum == k) {
                    max = i + 1;
                } else if (map.containsKey(sum - k)) {
                    max = Math.max(max, i - map.get(sum - k));
                }
                if (!map.containsKey(sum)) {
                    map.put(sum, i);
                }
            }
            return max;
        }
    }

}