209. Minimum Size Subarray Sum【滑动窗口】

Given an array of n positive integers and a positive integer s, find the minimal length of a contiguous subarray of which the sum ≥ s. If there isn't one, return 0 instead.

Example:

Input: s = 7, nums = [2,3,1,2,4,3]
Output: 2
Explanation: the subarray [4,3] has the minimal length under the problem constraint.
Follow up:
If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).

---

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        if(nums.length == 0 || nums == null) return 0;
        int n = nums.length;
        int left = 0, sum = 0, res = Integer.MAX_VALUE;
        for(int i=0; i<n; i++){
            sum += nums[i];
            while(sum >= s){
                res = Math.min(res, i-left+1);
                sum -= nums[left++];
            }
        }
       return res == Integer.MAX_VALUE ? 0 : res;
    }
}