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.

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;
}
};