Longest Palindromic Substring 用KMP解决

最新推荐文章于 2020-06-07 16:37:52 发布

xjwowangran

最新推荐文章于 2020-06-07 16:37:52 发布

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本文详细介绍了如何运用KMP算法解决最长回文子串问题，通过生成逆序字符串并进行KMP匹配，有效找到给定字符串中最长的回文子串。代码实现包括获取前缀函数、字符串比较、回文子串搜索等功能。

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Longest Palindromic Substring 用KMP解决

s求逆，依次KMP比较记录最大的匹配长度，O（n^2

// Palindromic.cpp : 定义控制台应用程序的入口点。
//

#include "stdafx.h"
#include <string>
#include <iostream>
using namespace std;
/*s:babcbabcbaccba
s0:abccabcbabcbab
s1:bccabcbabcbab
s2:ccabcbabcbab
……
     
  maxLen

*/
 void GetNext(string s, int slen, int* next)
 {
	 int i = 0,j = -1;
	 next[i] = -1;
	 while(i < slen - 1)
	 {
		 if(j == -1 || s[i] == s[j])
		 {
			 ++ i;
			 ++ j;
			 if(s[i] != s[j])
				 next[i] = j;
			 else 
				 next[i] = next[j];
		 }
		 else
			 j = next[j];

	 }

 }
 int Compare(string suffix, int sufflen, string s, int slen, int* next)
 {
	 int i = 0, j = -1, maxlen = 0;
	 while(i < slen && j < sufflen)
	 {
		 if(j == -1 || s[i] == suffix[j])
		 {
			 ++ i;
			 ++ j;
		 }else
			 j = next[j];
		 if(j > maxlen)
			 maxlen = j;
	 }
	 return maxlen;
	
 }

 string longestPalindrome(const string s, int slen)
 {
	 string s_reverse = s;
	 reverse(s_reverse.begin(), s_reverse.end());

	 string maxPattern = "";
	 int maxlen = 0, len;
	 for(int i=0; i < slen; ++ i)
	 {
		 string suffix = s_reverse.substr(i);
		 int* next = new int[suffix.size()];
		 if(suffix.size() < maxlen)
			break;
		 GetNext(suffix,suffix.size(), next);
		 len = Compare(suffix,suffix.size(), s, s.size(), next);

		 if(len > maxlen)
		 {
			 maxlen = len;
			 maxPattern = suffix.substr(0, len);
		 }
		 delete[] next;
	 }
	 return maxPattern;

 }




//===========================================================================
void Test(char* testName, const string s, string expected)
{
    if(testName != NULL)
        printf("%s begins: \n", testName);
	cout<<"s: "<< s<<endl;

    string result = longestPalindrome(s,s.size());

    if(expected == result)
        printf("passed.\n");
    else if(expected != result)
        printf("failed.\n");
   
	cout<<"result: "<<result<<endl;
}

// 空格在句子中间
void Test1()
{
    string s = "eraabaabcde";
	
    Test("Test1", s,"aabaa");

}
int _tmain(int argc, _TCHAR* argv[])
{
	Test1();
	return 0;
}

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