209. Minimum Size Subarray Sum

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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.
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.

解题思路：移动两个指针，指针之间的窗口保持比s大，通过移动两个指针寻找最小的size。

public class Solution {    public int minSubArrayLen(int s, int[] nums) {        int res = Integer.MAX_VALUE;        int i = 0, j = 0, sum = 0;        while (j < nums.length) {            sum += nums[j++];            while (sum >= s) {                res = Math.min(res, j-i);                sum -= nums[i++];            }        }        return res == Integer.MAX_VALUE ? 0 : res;    }}

class Solution {public:    int minSubArrayLen(int s, vector<int>& nums) {        int res = INT_MAX;        int i = 0, j = 0, sum = 0;        while (j < nums.size()) {            sum += nums[j++];            while (sum >= s) {                res = min(res, j-i);                sum -= nums[i++];            }        }        return res == INT_MAX ? 0 : res;    }};

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