209 Minimum Size Subarray Sum

Leetcode

Given an array of positive integers nums and a positive integer target, return the minimal length of a contiguous subarray [numsl, numsl+1, ..., numsr-1, numsr] of which the sum is greater than or equal to target. If there is no such subarray, return 0 instead.

Example 1:

Input: target = 7, nums = [2,3,1,2,4,3]
Output: 2
Explanation: The subarray [4,3] has the minimal length under the problem constraint.

Example 2:

Input: target = 4, nums = [1,4,4]
Output: 1

Example 3:

Input: target = 11, nums = [1,1,1,1,1,1,1,1]
Output: 0

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滑动窗口。左右两个指针，移动右指针给窗口加入元素，窗口所有元素和大于 target ，记录此时的长度，然后不断移动左指针直到窗口元素和小于 target

public int minSubArrayLen(int target, int[] nums) {
    int left=0, right=0;
    int min=Integer.MAX_VALUE;
    if(nums==null || nums.length==0) return min;
    int sum=0;
    while(right<nums.length || sum>=target){
        if(sum>=target){
            if(right-left<min) min=right-left;
            if(min==1) return 1;
            sum-=nums[left++];
        } else if (sum<target){
            sum+=nums[right++];
        } 
        
    }
    return min==Integer.MAX_VALUE?0:min;
}