algorithm/5.html at master · yji234/algorithm · GitHub

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<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>Document</title>
</head>
<body>
  <script>
    function longestPalindrome(s) {
      if(!s) {
        return '';
      }
      if(s.length === 1) {
        return s;
      }
      if(s.length === 2) {
        if(s.split('')[0] === s.split('')[1]) {
          return s;
        } else {
          return s.split('')[0];
        }
      }
      let sList = s.split('');
      let newSList = [];
      // yxy型
      let i = 1;
      while (i < sList.length) {
        if(sList[i-1] === sList[i+1]) {
          let step1 = 0;
          while (1) {
            let l = i-1-step1;
            let r = i+1+step1;
            if(sList[l] !== sList[r]) {
              let newS = sList.slice(l+1, r).join('');
              newSList.push(newS);
              // console.log(newSList)
              break;
            }
            if(l === 0 || r === sList.length-1) {
              if(sList[l] !== sList[r]) {
                let newS = sList.slice(l+1, r).join('');
                newSList.push(newS);
                // console.log(newSList)
                break;
              } else {
                let newS = sList.slice(l, r+1).join('');
                newSList.push(newS);
                // console.log(newSList)
                break;
              }
            }
            step1++;
          }
        }
        i++;
      }
      // xx型
      let j = 1;
      while (j < sList.length) {
        if(sList[j-1] === sList[j]) {
          let step2 = 0;
          while (1) {
            let l = j-2-step2;
            let r = j+1+step2;
            if(sList[l] !== sList[r]) {
              let newS = sList.slice(l+1, r).join('');
              newSList.push(newS)
              // console.log(newSList)
              break;
            }
            if(l === 0 || r === sList.length-1) {
              if(sList[l] !== sList[r]) {
                let newS = sList.slice(l+1, r).join('');
                newSList.push(newS)
                // console.log(newSList)
                break;
              } else {
                let newS = sList.slice(l, r+1).join('');
                newSList.push(newS)
                // console.log(newSList)
                break;
              }
            }
            step2++;
          }
        }
        j++;
      }
      // console.log(newSList)
      let list = newSList.sort(function (a, b) {
        return b.length-a.length;
      })
      if(list.length > 0) {
        return list[0]
      } else {
        return sList[0]
      }

    }
    // longestPalindrome('aba')
    // longestPalindrome('sabafs')
    // longestPalindrome('sabasd')
    // longestPalindrome('agabasd')
    // longestPalindrome('dabcbadl')
    // longestPalindrome('cbbd')
    // longestPalindrome('cbbcd')
    // longestPalindrome('adcbbcd')
    // longestPalindrome('cbbc')
    // console.log(longestPalindrome('asdcdffbabad'))
    // console.log(longestPalindrome(''))
    // longestPalindrome('cbbd')
    // console.log(longestPalindrome('cb'))
    console.log(longestPalindrome('abcda'))
  </script>
</body>
</html>