Minimum Size Subarray Sum

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.

More practice:

If you have figured out the O(n) solution, try coding another solution of which the time complexity is O(n log n).

Solution:

  1. public class Solution {
  2.   public int minSubArrayLen(int s, int[] a) {
  3.     if (a == null || a.length == 0)
  4.       return 0;
  6.     // i is slow pointer, j is fast pointer
  7.     int i = 0, j = 0, sum = 0, min = Integer.MAX_VALUE;
  9.     while (j < a.length) {
  10.       sum += a[j++];
  12.       while (sum >= s) {
  13.         min = Math.min(min, j - i);
  14.         sum -= a[i++];
  15.       }
  16.     }
  18.     return min == Integer.MAX_VALUE ? 0 : min;
  19.   }
  20. }