README.md

1312. Minimum Insertion Steps to Make a String Palindrome

Given a string s. In one step you can insert any character at any index of the string.

Return the minimum number of steps to make s palindrome.

A Palindrome String is one that reads the same backward as well as forward.

Example 1:

Input: s = "zzazz"
Output: 0
Explanation: The string "zzazz" is already palindrome we do not need any insertions.

Example 2:

Input: s = "mbadm"
Output: 2
Explanation: String can be "mbdadbm" or "mdbabdm".

Example 3:

Input: s = "leetcode"
Output: 5
Explanation: Inserting 5 characters the string becomes "leetcodocteel".

Constraints:

• 1 <= s.length <= 500
• s consists of lowercase English letters.

Solutions (Python)

1. Solution

from functools import cache


class Solution:
    def minInsertions(self, s: str) -> int:
        @cache
        def minInsertionsSub(i: int, j: int) -> int:
            if i >= j:
                return 0

            ret = 1 + minInsertionsSub(i + 1, j)
            ret = min(ret, 1 + minInsertionsSub(i, j - 1))
            if s[i] == s[j]:
                ret = min(ret, minInsertionsSub(i + 1, j - 1))

            return ret

        return minInsertionsSub(0, len(s) - 1)