Array - 209. Minimum Size Subarray Sum

209. Minimum Size Subarray Sum

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).

思路：

使用sliding window来做，一个指针遍历数组，一个指针记录起始位置。

代码：

java：

class Solution {

    public int minSubArrayLen(int s, int[] nums) {

        int from = 0, sum = 0, win = Integer.MAX_VALUE;
        for (int i = 0; i < nums.length; i++) {
            sum += nums[i];
            while (from <= i && sum >= s) {
                win = Math.min(win, i - from +1);
                sum -= nums[from++];
            }
        }
        return win == Integer.MAX_VALUE ? 0 : win;
    }
}