LeetCode-in-Java
1312. 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 don’t 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 <= 500sconsists of lowercase English letters.
Solution
public class Solution {
private int longestPalindrome(String a, String b, int n) {
int[][] dp = new int[n + 1][n + 1];
for (int i = 0; i < n + 1; i++) {
for (int j = 0; j < n + 1; j++) {
if (i == 0 || j == 0) {
dp[i][j] = 0;
} else if (a.charAt(i - 1) == b.charAt(j - 1)) {
dp[i][j] = 1 + dp[i - 1][j - 1];
} else {
dp[i][j] = Math.max(dp[i - 1][j], dp[i][j - 1]);
}
}
}
return dp[n][n];
}
public int minInsertions(String s) {
int n = s.length();
if (n < 2) {
return 0;
}
String rs = new StringBuilder(s).reverse().toString();
int l = longestPalindrome(s, rs, n);
return n - l;
}
}