g0301_0400.s0336_palindrome_pairs.Solution.kt Maven / Gradle / Ivy

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Kotlin-based LeetCode algorithm problem solutions, regularly updated

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package g0301_0400.s0336_palindrome_pairs

// #Hard #Array #String #Hash_Table #Trie #2022_11_17_Time_2451_ms_(67.33%)_Space_303.4_MB_(41.58%)

@Suppress("kotlin:S6218", "NAME_SHADOWING")
class Solution {
    fun palindromePairs(words: Array): List> {
        val ans = mutableListOf>()
        val root = TrieNode()
        for (idx in words.indices) {
            addWord(root, words[idx], idx)
        }
        for (idx in words.indices) {
            search(idx, root, words, ans)
        }
        return ans
    }

    private fun search(idxCurWord: Int, root: TrieNode, words: Array, res: MutableList>) {
        var cur: TrieNode? = root
        val curWord = words[idxCurWord]
        val lenW = curWord.length
        for (idxCh in curWord.indices) {
            if (cur!!.index >= 0 && cur.index != idxCurWord && isPalindrome(curWord, idxCh, lenW - 1))
                res.add(listOf(idxCurWord, cur.index))
            cur = cur.children[curWord[idxCh] - 'a']
            if (cur == null)
                return
        }
        for (idxPalin in cur!!.panlinIndicies) {
            if (idxPalin == idxCurWord) continue
            res.add(listOf(idxCurWord, idxPalin))
        }
    }

    private fun addWord(root: TrieNode, word: String, index: Int) {
        var cur: TrieNode? = root
        for (idx in word.indices.reversed()) {
            val idxCh = word[idx] - 'a'
            if (cur!!.children[idxCh] == null)
                cur.children[idxCh] = TrieNode()
            if (isPalindrome(word, 0, idx))
                cur.panlinIndicies.add(index)
            cur = cur.children[idxCh]
        }
        cur!!.panlinIndicies.add(index)
        cur.index = index
    }

    private fun isPalindrome(word: String, lo: Int, hi: Int): Boolean {
        var lo = lo
        var hi = hi
        while (lo < hi) {
            if (word[lo] != word[hi])
                return false
            ++lo
            --hi
        }
        return true
    }

    private data class TrieNode(
        val children: Array = Array(26) { null },
        var index: Int = -1,
        val panlinIndicies: MutableList = mutableListOf()
    )
}