LeetCode-in-Java

930. Binary Subarrays With Sum

Medium

Given a binary array nums and an integer goal, return the number of non-empty subarrays with a sum goal.

A subarray is a contiguous part of the array.

Example 1:

Input: nums = [1,0,1,0,1], goal = 2

Output: 4

Explanation: The 4 subarrays are bolded and underlined below:

[1,0,1,0,1]

[1,0,1,0,1]

[1,0,1,0,1]

[1,0,1,0,1]

Example 2:

Input: nums = [0,0,0,0,0], goal = 0

Output: 15

Constraints:

• 1 <= nums.length <= 3 * 104
• nums[i] is either 0 or 1.
• 0 <= goal <= nums.length

Solution

public class Solution {
    public int numSubarraysWithSum(int[] nums, int goal) {
        return goal == 0
                ? numSubarraysWithAtMostGoal(nums, 0)
                : numSubarraysWithAtMostGoal(nums, goal)
                        - numSubarraysWithAtMostGoal(nums, goal - 1);
    }

    private int numSubarraysWithAtMostGoal(int[] nums, int goal) {
        int windowSum = 0;
        int left = 0;
        int right = 0;
        int res = 0;
        while (right < nums.length) {
            windowSum += nums[right++];
            while (left < right && windowSum > goal) {
                windowSum -= nums[left++];
            }
            res += (right - left);
        }
        return res;
    }
}

This site is open source. Improve this page.