# 0325. Maximum Size Subarray Sum Equals k
###### tags: `Leetcode` `FaceBook` `Medium` `Prefix Sum` `HashMap`
Link: https://leetcode.com/problems/maximum-size-subarray-sum-equals-k/
## 思路 $O(N)$ $O(N)$
map记录prefix sum和他们最早出现的位置
## Code

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