LeetCode in Kotlin

3258. Count Substrings That Satisfy K-Constraint I

Easy

You are given a binary string s and an integer k.

A binary string satisfies the k-constraint if either of the following conditions holds:

• The number of 0’s in the string is at most k.
• The number of 1’s in the string is at most k.

Return an integer denoting the number of substrings of s that satisfy the k-constraint.

Example 1:

Input: s = “10101”, k = 1

Output: 12

Explanation:

Every substring of s except the substrings "1010", "10101", and "0101" satisfies the k-constraint.

Example 2:

Input: s = “1010101”, k = 2

Output: 25

Explanation:

Every substring of s except the substrings with a length greater than 5 satisfies the k-constraint.

Example 3:

Input: s = “11111”, k = 1

Output: 15

Explanation:

All substrings of s satisfy the k-constraint.

Constraints:

• 1 <= s.length <= 50
• 1 <= k <= s.length
• s[i] is either '0' or '1'.

Solution

class Solution {
    fun countKConstraintSubstrings(s: String, k: Int): Int {
        val n = s.length
        var sum = n
        var i = 0
        var j = 0
        var one = 0
        var zero = 0
        var ch: Char
        while (j < n) {
            ch = s[j++]
            if (ch == '0') {
                zero++
            } else {
                one++
            }
            while (i <= j && one > k && zero > k) {
                ch = s[i++]
                if (ch == '0') {
                    zero--
                } else {
                    one--
                }
            }
            val len = (zero + one - 1)
            sum += len
        }
        return sum
    }
}

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