Codesignal - buildPalindrome

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] 20 seconds (swift)
• [input] string stGuaranteed constraints:
  3 ≤ st.length ≤ 10.
• A string consisting of lowercase English letters.
• [output] string

설명

문자열을 palindrome으로 만들어라

 

풀이

주어진 문자열을 뒤집었을때 똑같으면 그대로 리턴

똑같지 않으면 같은 부분부터 이어붙여 리턴

예> abba -> abba => abba

​ Kebab -> babek => kebabek

func buildPalindrome(st: String) -> String {
    let reverse = String(st.reversed())
    var idx = 0
    var str = st

    if reverse == st {
        return st
    } else {
        for i in 1 ..< st.count {
            let original = st.suffix(i)
            let compare = String(original.reversed())

            if original == compare {
                idx = i
            }
        }

        str += String(reverse[reverse.index(reverse.startIndex, offsetBy: idx)...])
    }

    return str
}

다른 사람 풀이

func buildPalindrome(st: String) -> String {
    let sr = String(st.characters.reversed())
    if st == sr {
        return st
    } else {
        return String(st[st.startIndex]) + buildPalindrome(st: String(st.characters.dropFirst())) + String(st[st.startIndex])
    }
}