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1437. Minimum Insertion Steps To Make A String Palindrome

String Dynamic Programming

Problem - Minimum Insertion Steps To Make A String Palindrome

Hard

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

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class Solution:
    def minInsertions(self, s: str) -> int:
        n = len(s)
        dp = [[0] * n for _ in range(n)]

        for i in range(n - 2, -1, -1):
            for j in range(i + 1, n):
                if s[i] == s[j]:
                    dp[i][j] = dp[i + 1][j - 1]
                else:
                    dp[i][j] = min(dp[i + 1][j], dp[i][j - 1]) + 1

        return dp[0][-1]

Submission Stats:

  • Runtime: 307 ms (91.80%)
  • Memory: 19.5 MB (55.97%)