209. Minimum Size Subarray Sum

class Solution {
public:
    int minSubArrayLen(int s, vector<int>& nums) {
        int w = 0, _sum = 0, res = INT_MAX;
        for (int i = 0; i < nums.size(); i++) {
            _sum += nums[i];
            while (w <= i && _sum >= s) {
                res = min(res, i-w+1);
                _sum -= nums[w];
                w++;
            }
        }
        return res == INT_MAX ? 0 : res;
    }
};