LeetCode in Kotlin

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

class Solution {
    fun numSubarraysWithSum(nums: IntArray, goal: Int): Int {
        return atmostK(nums, goal) - atmostK(nums, goal - 1)
    }

    fun atmostK(arr: IntArray, k: Int): Int {
        var cnt = 0
        var i = 0
        var j = 0
        var sum = 0
        while (j < arr.size) {
            sum += arr[j]
            if (sum > k) {
                while (i <= j && sum > k) {
                    sum -= arr[i]
                    i++
                }
            }
            cnt += j - i + 1
            j++
        }
        return cnt
    }
}

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