LeetCode209 Minimum Size Subarray Sum

题目：

       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). 

public class MinimumSizeSubarraySum {
    public static int minSubArrayLen(int s, int[] nums) {
        if (nums==null || nums.length == 0)
            return 0;
        int l = 0, r = -1;//nums[l...r]为滑动窗口
        int sum = 0;
        int res = nums.length + 1;

        while (l < nums.length) {
            if (r + 1 < nums.length && sum < s) {
                sum += nums[++r];
            } else {
                sum -= nums[l++];
            }
            if (sum >= s) {
                res = Math.min(res, r - l + 1);
            }
        }
        return res == nums.length + 1 ? 0 : res;
    }

    public static void main(String[] args) {
        int[] nums = {1, 2, 3, 4, 5};
        int s = 11;
        System.out.println(minSubArrayLen(s, nums));
    }
}