最长回文
Time Limit: 4000/2000 MS (Java/Others) Memory Limit: 32768/32768 K (Java/Others) Total Submission(s): 23931 Accepted Submission(s): 8761
Problem Description
给出一个只由小写英文字符a,b,c...y,z组成的字符串S,求S中最长回文串的长度.
回文就是正反读都是一样的字符串,如aba, abba等
Input
输入有多组case,不超过120组,每组输入为一行小写英文字符a,b,c...y,z组成的字符串S
两组case之间由空行隔开(该空行不用处理)
字符串长度len <= 110000
Output
每一行一个整数x,对应一组case,表示该组case的字符串中所包含的最长回文长度.
Sample Input
aaaa
abab
Sample Output
4
3
Source
2009 Multi-University Training Contest 16 - Host by NIT
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直接贴代码吧
#include <iostream>
#include <cstdio>
#include <cmath>
#include <cstring>
using namespace std;
const int maxn = 110000+5;
char s[maxn],s1[maxn<<1];
int a[maxn<<1];
int i,j,k,max_right,pos,len,new_len;
void init(){
//构建新的字符串
len = strlen(s);
pos = 0;
new_len = 0;
s1[0]='*';
for (i=0; i<len; i++){
s1[++new_len] = '#';
s1[++new_len] = s[i];
}
s1[++new_len] = '#';
}
int manacher(){
int MAX = -1;
for (i=2; i<2*len+1; i++) {
if (a[pos]+pos>i) a[i] = min(a[pos*2-i],a[pos]+pos-i);
else a[i] = 1;
while (s1[i-a[i]]==s1[i+a[i]]) a[i]++;
if (pos+a[pos]<i+a[i]) pos = i;
MAX = max(MAX,a[i]);
}
return MAX-1;
}
int main(){
while (scanf("%s",s)!=EOF){
init();
printf("%d\n",manacher());
}
return 0;
}
