325

class Solution {
public:
    int maxSubArrayLen(vector<int>& nums, int k) {
        if (nums.empty()) return 0;
        unordered_map<int,int>entry;
        int res = 0, sum = 0, n = nums.size();
        for (int i = 0; i < n; i++){
            sum += nums[i];
            if (sum == k)
                res = i+1;
            else if (entry.count(sum-k))
                res = max(res, i-entry[sum-k]);
            if (!entry.count(sum))
                entry[sum] = i;
        }
        return res;
    }
};