DEV Community

Prashant Mishra
Prashant Mishra

Posted on • Originally published at


Minimum Insertion steps needed to make a string palindrome (Same as LCS)

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 don't need any insertions. 
Enter fullscreen mode Exit fullscreen mode

Tabulation approach
Time complexity : O(n*m), space complexity : o(n*m) for dp array

class Solution {
    public int minInsertions(String s) {
        //going with the hint given 
        //i.e. finding length of the longest palindromic subsequence x
        //now , s.length()-x = n ,so n insertion are needed to make the entire string as palindromic string
        String r = new StringBuilder(s).reverse().toString();
        int dp[][] = new int[s.length()+1][r.length()+1];// 1 based indexing
        for(int i =0;i<=s.length();i++){
            dp[i][0] =0;
            dp[0][i] =0;
        for(int  i =1;i<=s.length();i++){
            for(int j=1;j<=r.length();j++){
                    dp[i][j] = 1 + dp[i-1][j-1];
                else dp[i][j] = Integer.max(dp[i][j-1],dp[i-1][j]);
        return s.length() - dp[s.length()][r.length()];
Enter fullscreen mode Exit fullscreen mode

Latest comments (0)

An Animated Guide to Node.js Event Loop

Node.js doesn’t stop from running other operations because of Libuv, a C++ library responsible for the event loop and asynchronously handling tasks such as network requests, DNS resolution, file system operations, data encryption, etc.

What happens under the hood when Node.js works on tasks such as database queries? We will explore it by following this piece of code step by step.