【Leetcode】Minimum Size Subarray Sum

题目链接：https://leetcode.com/problems/minimum-size-subarray-sum/

题目：

Given an array of n positive integers and a positive integer s, find the minimal length of a subarray of which the sum ≥ s. If there isn't one, return 0 instead.

For example, given the array [2,3,1,2,4,3] and s = 7,
the subarray [4,3] has the minimal length under the problem constraint.

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More practice:

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：

用两个游标表示当前范围，若满足条件则更新最小长度，否则游标做出相应调整。

算法：

	public int minSubArrayLen(int s, int[] nums) {
		if (nums.length == 0)
			return 0;
		int minLen = Integer.MAX_VALUE, start = 0, end = 0;
		int sum = 0;
		while (end < nums.length) {
			while (sum < s && end < nums.length) {
				sum += nums[end++];//若不满足 则扩大范围
			}
			while (sum >= s && start < end) {
				minLen = Math.min(minLen, end - start);
				sum -= nums[start++];//当满足条件后    start增大看是否还存在更小长度
			}
		}
		if (minLen == Integer.MAX_VALUE) {
			minLen = 0;
		}
		return minLen;
	}