滑动窗口应用场景：

最长连续子串等、最小和连续子集等问题，和动规的区别是动规可以划分出子集；

思维导图：

举例：

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: 2Explanation: 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). 

代码：

public class Solution {

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

        if(nums.length==0) return -1;

        int i=0,j=0;int min = Integer.MAX_VALUE,sum=0;

        for(i=0;i<nums.length;i++){

            //sum = nums[i];

            while(j<nums.length&&sum<s){

                sum+=nums[j];

                j++;                

            }

            if(sum>=s)//排除j>=n跳出循环的情况

                min = Math.min(min,j-i);            

            sum-=nums[i];

        }

        return min==Integer.MAX_VALUE? -1: min;//边界条件考虑，为空的时候，无解的时候

    }

}