manacher（求最大回文串并返回）

 leetcode(medium)

5. Longest Palindromic Substring

Medium

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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"

复杂度0（n）

#include<iostream>
#include<algorithm>
#include<cstring>
using namespace std;
const int k =1000001;
char ma[k] ;
int mp[k];
string manacher(string s)
{
string * k=s;
int l=0;int len;len=strlen(k);
ma[l++]='$';
ma[l++]='#';
for(int i=0;i<len;i++)
{
ma[l++]=s[i];
ma[l++]='#';
}
ma[l]=0;
int mx=0,id=0,reslen=0,rescenter=0;
for(int i=0;i<l;i++)
{
mp[i]=mx>i?min(mp[2*id-1],mx-i):1;//利用以知，有动态规划思想
while(ma[i+mp[i]]==ma[i-mp[i]])mp[i]++;
if(i+mp[i]>mx)
{
mx=i+mp[i];
id=i;
}
if(reslen<mp[i])
{
reslen=mp[i];
rescenter=i;
}
}
return s.substr((rescenter-reslen)/2,reslen-1);
}
int main()
{
string s,t;
while(cin>>s)
{
t=manacher(s);
cout<<t<<endl;
}
}