leetCode-05 《最长回文子串》

最长回文子串

暴力枚举法

const forceMethod = (str) => {
  if (str.length < 2) return str
  let cur = 0
  let max = 1

  const judge = (s) => {
    let l = 0
    let r = s.length - 1

    while (l < r) { // 到l > r的时候会跳出循环
      if (s[l] !== s[r]) {
        return false
      }
      l++
      r--
    }
    return true
  }

  for (let i = 0; i < str.length; i++) {
    for (let j = i + 1; j < str.length; j++) {
      let curStr = str.slice(i, j + 1)
      if (judge(curStr) && curStr.length > max) {
        cur = i
        max = curStr.length
      }
    }
  }
  console.log(cur, max)
  return str.substr(cur, max)
}

中心扩散法

const longestPalindrome = str => {
  if (str.length < 2) return str

  let start = 0
  let maxLen = 1

  // 判断函数
  const judge = (left, right) => {
    while (left >= 0 && right < str.length && str[left] === str[right]) { // 说明满足条件
      if (right - left + 1 > maxLen) {
        maxLen = right - left + 1
        start = left
      }
      left--
      right++
    }
  }


  for (let i = 0; i < str.length; i++) {
    judge(i - 1, i + 1) // 奇数
    judge(i, i + 1) // 偶数
  }

  return str.slice(start, start + maxLen)
}