最长回文子串问题 Manacher(马拉车)算法模板

#include <iostream>
#include <cstdio>
#include <cstring>
#define Min(a,b) a>b?b:a
#define Max(a,b) a>b?a:b
using namespace std;
int Len[3000005];
char str[3000005],s[3000005];
int n,mx,id,len;
 
void init(){
    
    
    memset(str,0,sizeof(str));
    int k=0;
    str[k++] = '$';
    for(int i=0;i<len;i++){
    
    
        str[k++]='#';
        str[k++]=s[i];
    }
    str[k++]='#';
    len=k;
}
 
int Manacher(){
    
    
  Len[0] = 0;
  int sum = 0;
  mx = 0;
  for(int i=1;i<len;i++){
    
    
    if(i < mx) Len[i] = Min(mx - i, Len[2 * id - i]);
    else Len[i] = 1;
    while(str[i - Len[i]]== str[i + Len[i]]) Len[i]++;
    if(Len[i] + i > mx){
    
    
      mx = Len[i] + i;
      id = i;
      sum = Max(sum, Len[i]);
    }
  }
  return (sum - 1);
}
 
int main()
{
    
    
  scanf("%d",&n);
  while(n--){
    
    
    scanf("%s",s);
    len = strlen(s);
    init();
    int temp = Manacher();
    printf("%d\n",temp);
  }
  return 0;
}