0209. Minimum Size Subarray Sum

https://leetcode.com/problems/minimum-size-subarray-sum

Description

Given an array of positive integers nums and a positive integer target, return the minimal length of a contiguous subarray [numsl, numsl+1, ..., numsr-1, numsr] of which the sum is greater than or equal to target. If there is no such subarray, return 0 instead.

Example 1:

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

Example 2:

**Input:** target = 4, nums = [1,4,4]
**Output:** 1

Example 3:

**Input:** target = 11, nums = [1,1,1,1,1,1,1,1]
**Output:** 0

Constraints:

• 1 <= target <= 109

• 1 <= nums.length <= 105

• 1 <= nums[i] <= 105

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)).

ac1: Sliding window

class Solution {
    public int minSubArrayLen(int s, int[] nums) {
        // edge cases
        if (nums == null || nums.length == 0 || s <= 0) {
            return 0;
        }

        int l = 0, r = 0, sum = 0, min = Integer.MAX_VALUE;
        for (;r < nums.length; r++) {
            sum += nums[r];

            while (sum >= s) {
                min = Math.min(min, r - l + 1);
                sum -= nums[l];
                l++;
            }
        }

        return min == Integer.MAX_VALUE ? 0 : min;
    }
}
// O(N) time, O(1) space

ac2: Binary search in prefix sum array