LeetCode-in-All

131. Palindrome Partitioning

Medium

Given a string s, partition s such that every substring of the partition is a palindrome. Return all possible palindrome partitioning of s.

A palindrome string is a string that reads the same backward as forward.

Example 1:

Input: s = “aab”

Output: [[“a”,”a”,”b”],[“aa”,”b”]]

Example 2:

Input: s = “a”

Output: [[“a”]]

Constraints:

• 1 <= s.length <= 16
• s contains only lowercase English letters.

Solution

@Suppress("NAME_SHADOWING")
class Solution {
    fun partition(s: String): List<List<String>> {
        val res = ArrayList<List<String>>()
        val mem = Array(s.length) { IntArray(s.length) }

        fun isPalindrome(i: Int, j: Int): Boolean {
            if (i > j) {
                return true
            }
            return when (mem[i][j]) {
                1 -> true
                2 -> false
                else -> {
                    val res = s[i] == s[j] && isPalindrome(i + 1, j - 1)
                    mem[i][j] = if (res) 1 else 2
                    res
                }
            }
        }

        fun dfs(start: Int, path: ArrayList<String>) {
            if (start == s.length) {
                res.add(path.toList())
                return
            }

            for (i in start..s.length - 1) {
                if (!isPalindrome(start, i)) {
                    continue
                }
                path.add(s.substring(start..i))
                dfs(i + 1, path)
                path.removeAt(path.size - 1)
            }
        }
        dfs(0, ArrayList())
        return res
    }
}

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