LeetCode-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). 

 

使用双指针，记录当前位置，和开始位置，通过移动两个指针，滑动窗口，时间复杂度O(n)

public int minSubArrayLen(int s, int[] nums) {//my 
        int sum =0;
        int index = 0;//当前子序列开始的位置
        int len =nums.length+1;//最小长度
        for(int i =0;i<nums.length;i++){
            sum += nums[i];
            while(sum>=s){//如果sum>=s则左指针向右滑动
                if((i-index+1)<len){
                    len = i-index+1;
                }
                sum -= nums[index];
                index++;
            }
        }
        return len>nums.length?0:len;
    }