mateusz58
6/11/2019 - 9:26 PM

Palindrome

Given a string, find the shortest possible string which can be achieved by adding characters to the end of initial string to make it a palindrome.

Example

For st = "abcdc", the output should be buildPalindrome(st) = "abcdcba".

Input/Output

[execution time limit] 3 seconds (java)

[input] string st

A string consisting of lowercase English letters.

Guaranteed constraints: 3 ≤ st.length ≤ 10.

[output] string

[Java] Syntax Tips

// Prints help message to the console // Returns a string // // Globals declared here will cause a compilation error, // declare variables inside the function instead! String helloWorld(String name) { System.out.println("This prints to the console when you Run Tests"); return "Hello, " + name; }

palindrome
content_copyfile_download
String buildPalindrome(String s) {
    for (int i = 0; i < s.length(); i++) {
        if (isPalindrome(s.substring(i))) {
            StringBuilder sb = new StringBuilder();
            sb.append(s);
            for (int j = i - 1; j >= 0; j--) {
                sb.append(s.charAt(j));
            }
            return sb.toString();
        }
    }
    // Guaranteed not to get here
    //
    return "";
}

boolean isPalindrome(String s) {
    // Walk the string from head to tail
    // comparing characters at each side as we go
    //
    int h = 0;
    int t = s.length() - 1;
    while (h < t) {
        if (s.charAt(h) != s.charAt(t)) {
            return false;
        }
        h++;
        t--;
    }
    return true;
}