LeetCode-5. Longest Palindromic Substring

Given a string s, find the longest palindromic substring in s. You may assume that the maximum length of s is 1000.

Example 1:

Input: "babad"
Output: "bab"
Note: "aba" is also a valid answer.

Example 2:

Input: "cbbd"
Output: "bb"

题解：

class Solution {
public:
  string longestPalindrome(string s) {
    int n = s.length();
    if (n < 2) {
      return s;
    }
    int maxi = 1, begin = 0;
    for (int i = 0; i < n; i++) {
      if (s[i] == s[i + 1]) {
        int j = i, k = i + 1;
        while (s[j] == s[k] && j >= 0 && k < n) {
          k++;
          j--;
        }
        maxi = max(maxi, k - j - 1);
        if (maxi == k - j - 1) {
          begin = j + 1;
        }
      }
      if (i >= 1 && s[i - 1] == s[i + 1]) {
        int j = i - 1, k = i + 1;
        while (s[j] == s[k] && j >= 0 && k < n) {
          k++;
          j--;
        }
        maxi = max(maxi, k - j - 1);
        if (maxi == k - j - 1) {
          begin = j + 1;
        }
      }
    }
    string ans = s.substr(begin, maxi);
    return ans;
  }
};