Lintcode 406. 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 -1 instead.

Example

Example 1:

Input: [2,3,1,2,4,3], s = 7
Output: 2
Explanation: The subarray [4,3] has the minimal length under the problem constraint.

Example 2:

Input: [1, 2, 3, 4, 5], s = 100
Output: -1

Challenge

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

Code (Java):

public class Solution {
    /**
     * @param nums: an array of integers
     * @param s: An integer
     * @return: an integer representing the minimum size of subarray
     */
    public int minimumSize(int[] nums, int s) {
        if (nums == null || nums.length == 0) {
            return -1;
        }
        
        int minLen = Integer.MAX_VALUE;
        int sum = 0;
        int left = 0;
        
        for (int right = 0; right < nums.length; right++) {
            sum += nums[right];
            
            while (sum >= s) {
                minLen = Math.min(minLen, right - left + 1);
                sum -= nums[left];
                left++;
            }
        }
        
        return minLen == Integer.MAX_VALUE ? -1 : minLen;
    }
}