题目：

题解：

func longestPalindrome(s string) string {if s == "" {return ""}start, end := 0, 0for i := 0; i < len(s); i++ {left1, right1 := expandAroundCenter(s, i, i)left2, right2 := expandAroundCenter(s, i, i + 1)if right1 - left1 > end - start {start, end = left1, right1}if right2 - left2 > end - start {start, end = left2, right2}}return s[start:end+1]
}func expandAroundCenter(s string, left, right int) (int, int) {for ; left >= 0 && right < len(s) && s[left] == s[right]; left, right = left-1 , right+1 { }return left + 1, right - 1
}