Minimum Size Subarray Sum 解答

Question

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.

Solution 1 -- Two Pointers

Following the thought of slide window, we apply two pointers here to solve the problem, one for left and one for right.

If current sum >= target, left++;

If current sum < target, right--;

Remember to check right index before getting nums[right], and sum value is nums[0] at beginning.

Time complexity O(n).

 1 public class Solution {
 2     public int minSubArrayLen(int s, int[] nums) {
 3         if (nums == null || nums.length == 0)
 4             return 0;
 5         int length = nums.length, left = 0, right = 0, result = length, sum = nums[0];
 6         while (right < length) {
 7             if (left == right) {
 8                 if (nums[left] >= s) {
 9                     return 1;
10                 } else {
11                     right++;
12                     if (right < length)
13                         sum += nums[right];
14                     else
15                         break;
16                 }
17             } else {
18                 if (sum < s) {
19                     right++;
20                     if (right < length)
21                         sum += nums[right];
22                     else
23                         break;
24                 } else {
25                     result = Math.min(result, right - left + 1);
26                     sum -= nums[left];
27                     left++;
28                 }
29             }
30         }
31         if (left == 0 && sum < s)
32             result = 0;
33         return result;
34     }
35 }