LeetCode-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.

Analysis:

Two pointers method, as the prefix array is already monotoic, we just keep sum[p2]-sum[p1]>=s, whenever p1 = p1+1, we move p2 correspondingly.

 

Solution:

public class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        if (nums==null || nums.length==0) return 0;
        int minLen = 0;
        int p1 = 0;
        int p2 = 1;
        int sum = nums[p1];
        while (sum < s && p2<nums.length){
            sum += nums[p2++];
        }
        if (sum<s && p2>=nums.length) return minLen;
        minLen = p2 - p1;
 
        while (p1<nums.length){
            p1++;
            sum -= nums[p1-1];
            while (sum<s && p2 < nums.length){
                sum += nums[p2++];
            }
            if (p2==nums.length && sum<s) break;
            if (sum>=s) minLen = Math.min(p2-p1, minLen);
        }

        return minLen;
    }
}