LeetCode in Kotlin

2213. Longest Substring of One Repeating Character

Hard

You are given a 0-indexed string s. You are also given a 0-indexed string queryCharacters of length k and a 0-indexed array of integer indices queryIndices of length k, both of which are used to describe k queries.

The ith query updates the character in s at index queryIndices[i] to the character queryCharacters[i].

Return an array lengths of length k where lengths[i] is the length of the longest substring of s consisting of only one repeating character after the ith query is performed.

Example 1:

Input: s = “babacc”, queryCharacters = “bcb”, queryIndices = [1,3,3]

Output: [3,3,4]

Explanation: - 1^st query updates s = “bbbacc”. The longest substring consisting of one repeating character is “bbb” with length 3.

• 2^nd query updates s = “bbbccc”. The longest substring consisting of one repeating character can be “bbb” or “ccc” with length 3.

• 3^rd query updates s = “bbbbcc”. The longest substring consisting of one repeating character is “bbbb” with length 4.

Thus, we return [3,3,4].

Example 2:

Input: s = “abyzz”, queryCharacters = “aa”, queryIndices = [2,1]

Output: [2,3]

Explanation: - 1^st query updates s = “abazz”. The longest substring consisting of one repeating character is “zz” with length 2.

• 2^nd query updates s = “aaazz”. The longest substring consisting of one repeating character is “aaa” with length 3.

Thus, we return [2,3].

Constraints:

• 1 <= s.length <= 105
• s consists of lowercase English letters.
• k == queryCharacters.length == queryIndices.length
• 1 <= k <= 105
• queryCharacters consists of lowercase English letters.
• 0 <= queryIndices[i] < s.length

Solution

class Solution {
    private lateinit var ca: CharArray

    fun longestRepeating(s: String, queryCharacters: String, queryIndices: IntArray): IntArray {
        ca = s.toCharArray()
        val result = IntArray(queryIndices.size)
        val root = SegmentTree(0, ca.size)
        for (i in queryIndices.indices) {
            ca[queryIndices[i]] = queryCharacters[i]
            root.update(queryIndices[i])
            result[i] = root.longest
        }
        return result
    }

    private inner class SegmentTree(val start: Int, val end: Int) {
        var longest: Int = 0
        var leftLength: Int = 0
        var rightLength: Int = 0
        private lateinit var left: SegmentTree
        private lateinit var right: SegmentTree

        init {
            if (end - start > 1) {
                val mid = (start + end) / 2
                left = SegmentTree(start, mid)
                right = SegmentTree(mid, end)
                merge()
            } else {
                longest = 1
                leftLength = 1
                rightLength = 1
            }
        }

        fun update(index: Int) {
            if (end - start == 1) return
            if (index < (left.end)) {
                left.update(index)
            } else {
                right.update(index)
            }
            merge()
        }

        private fun merge() {
            longest = maxOf(left.longest, right.longest)
            if (ca[left.end - 1] == ca[right.start]) {
                longest = maxOf(longest, left.rightLength + right.leftLength)
                leftLength = if (left.leftLength == left.end - left.start) {
                    left.leftLength + right.leftLength
                } else {
                    left.leftLength
                }
                rightLength = if (right.rightLength == (right.end - right.start)) {
                    right.rightLength + left.rightLength
                } else {
                    right.rightLength
                }
            } else {
                leftLength = left.leftLength
                rightLength = right.rightLength
            }
        }
    }
}

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