Palindrome

Palindrome

Palindrome이란 앞뒤로 뒤집어도 같은 문자열을 Palindrome이라고 한다.

Palindrome인지 판별하는 함수

function isPalin(s) {
    const mid = Math.floor(s.length / 2);
    for(let i = 0; i < mid; i++) {
      if(s[i] !== s[s.length -1 - i]) {
        return false;
      }
    }
    return true;
  }

일단 문자열의 중간을 구한 뒤 중간을 기준으로 첫글자와 마지막 글자를 비교해

한번이라도 일치하지 않으면 false를 반환한다.

function isPalin(s) {
  for(let i = 0; i < s.length; i++) {
    s = s.toLowerCase().replace(/a-z/g, '');
    if(s.split('').reverse() !== s) {
      return false;
  }
  return true;
}

특수문자나 숫자 등을 제외한 뒤 판별하는 함수이다.

부분 문자열 중 가장 긴 Palindrome을 구하기

let longestPalindrome = function (str) {
  // TODO: 여기에 코드를 작성합니다.
  if(str.length <= 1) return str.length;
  for(let i = str.length; i > 0; i--) {
    for(let j = 0; j <= str.length -i; j++) {
      const isPal = isPalin(str.slice(j, i + j))
      if(isPal) return i
    }
  }
  function isPalin(s) {
    const mid = Math.floor(s.length / 2);
    for(let i = 0; i < mid; i++) {
      if(s[i] !== s[s.length -1 - i]) {
        return false;
      }
    }
    return true;
  }
};

함수에 'My dad is a racecar athlete'를 대입해 콘솔 찍어 보면...
There is a tattarrattat
There is a tattarratta
here is a tattarrattat
There is a tattarratt
here is a tattarratta
ere is a tattarrattat
There is a tattarrat
here is a tattarratt
ere is a tattarratta
re is a tattarrattat
There is a tattarra
here is a tattarrat
ere is a tattarratt
re is a tattarratta
e is a tattarrattat
There is a tattarr
here is a tattarra
ere is a tattarrat
re is a tattarratt
e is a tattarratta
is a tattarrattat
There is a tattar
here is a tattarr
ere is a tattarra
re is a tattarrat
e is a tattarratt
is a tattarratta
is a tattarrattat
There is a tatta
here is a tattar
ere is a tattarr
re is a tattarra
e is a tattarrat
is a tattarratt
is a tattarratta
s a tattarrattat
There is a tatt
here is a tatta
ere is a tattar
re is a tattarr
e is a tattarra
is a tattarrat
is a tattarratt
s a tattarratta
a tattarrattat
There is a tat
here is a tatt
ere is a tatta
re is a tattar
e is a tattarr
is a tattarra
is a tattarrat
s a tattarratt
a tattarratta
a tattarrattat
There is a ta
here is a tat
ere is a tatt
re is a tatta
e is a tattar
is a tattarr
is a tattarra
s a tattarrat
a tattarratt
a tattarratta
tattarrattat
There is a t
here is a ta
ere is a tat
re is a tatt
e is a tatta
is a tattar
is a tattarr
s a tattarra
a tattarrat
a tattarratt
tattarratta
tattarrattat

요렇게 나온다...정말 대단한 것 같다..