209. Minimum Size Subarray Sum

Given an array of positive integers nums and a positive integer target, return the minimal length of a subarray whose 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

My Solutions: 这道题和76相似。用sliding window记录大于等于target的范围，如果超过了target，可以把sliding window的左边向右移动。

Time: O(n); Space: O(1)

public int minSubArrayLen(int target, int[] nums) {
    int min = nums.length + 1, l = 0, sum = 0;
    for (int i = 0; i < nums.length; i++) {
        sum += nums[i];
        while (sum >= target) {
            min = Math.min(min, i - l + 1);
            // remove the first element from the window
            sum -= nums[l];
            // move the start of window --> left
            l++;
        }
    }
    return min > nums.length ? 0 : min;
}