Longest Palindromic Substring

最新推荐文章于 2021-11-16 22:29:32 发布

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本文介绍了一种寻找字符串中最长回文子串的有效算法。通过动态规划的方法，该算法能够处理长度达1000的字符串，并快速找出符合条件的最长回文子串。文章包含完整的C++代码实现及两个示例。

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

Example:

Input: "babad"

Output: "bab"

Note: "aba" is also a valid answer.

Example:

Input: "cbbd"

Output: "bb"

class Solution {
public:
    string longestPalindrome(string s) {
        if (s.empty())
        {
            return "";
        }
        if (1 == s.size())
        {
            return s;
        }
        int maxLen = 0;
        int len = s.size();
        int table[len][len] = {0};
        
        for (int i = 0; i < len; i++)
        {
            table[i][i] = 1;
        }
        string longstr = s.substr(0, 1);
        maxLen = 1;
        for (int i = 0; i < (len - 1); i++)
        {
            if (s[i] == s[i + 1])
            {
                table[i][i+1] = 1;
                maxLen = 2;
                longstr = s.substr(i, maxLen);                
            }
            else
            {
                table[i][i+1] = 0;
            }
        }
        
        
       for (int l = 3; l <= len; l++)
       {
           for (int i = 0; i <= (len - l); i++)
           {
               int j = i + l - 1;
               if (s[i] == s[j])
               {
                   table[i][j] = table[i + 1][ j - 1];
                   if (table[i][j] == 1 && l > maxLen) 
                   {
                       maxLen = j + 1 - i;
                       longstr = s.substr(i, maxLen);                                              
                   }
                        
               }
               else
               {
                   table[i][j] = 0;
               }
           }
       }
    
       return longstr;
        
        
    }
};