209. Minimum Size Subarray Sum
摘要：
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...
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.
Example:
Input: s = 7, nums = [2,3,1,2,4,3]
Output: 2
Explanation: the subarray [4,3] has the minimal length under the problem constraint.
Follow up:
If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).
難度：medium
題目：
給定一個包含正整數的陣列和一個正整數s，找出最小長度且元素相連的子陣列使得其和大於s. 如果不存在這樣的子陣列，則返回0.
思路：
滑動伸縮視窗。滑動視窗左邊界為start index, 右邊界為i, 視窗為[start index, i].
Runtime: 2 ms, faster than 99.88% of Java online submissions for Minimum Size Subarray Sum.
class Solution {
// O(2n)
public int minSubArrayLen(int s, int[] nums) {
int sum = 0, startIdx = 0;
int minLen = nums.length + 1;
for (int i = 0; i < nums.length; i++) {
sum += nums[i];
if (sum >= s) {
// shrink window
while (startIdx <= i && sum >= s) {
minLen = Math.min(minLen, i - startIdx + 1);
sum -= nums[startIdx++];
}
}
}
return minLen > nums.length ? 0 : minLen;
}
}