209. 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.

样例

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.

解答

我们需要两个指针，一个指向区间开头，一个结尾，开始时，两个指针都在区间开头，然后递增尾指针，这样我们就可以找到一个区间，使区间和大于等于s,然后头指针递增头指针，缩小区间。最后重复上述过程。

int minSubArrayLen(int s, vector<int>& nums) {    if (nums.size() == 0)        return 0;    vector<int>::size_type start = 0, end = 0,len = nums.size(), res = nums.size() + 1;    int sum = 0;    while (end < nums.size()) {        while (sum < s && end < len)            sum = sum + nums[end++];        if (sum < s)            break;        while (sum >= s && start < end)            sum = sum - nums[start++];        res = min(res, end - start + 1);    }    if (res == nums.size() + 1)        return 0;    return res;}