Codeforces Round #253 (Div. 2) B - Kolya and Tandem Repeat

本题要考虑字符串本身就存在tandem，

如测试用例

aaaaaaaaabbb

3

输出结果应该是8而不是6，因为字符串本身的tanderm时最长的

故要考虑字符串本身的最大的tanderm和添加k个字符后最大的tanderm

#include <iostream>
#include <vector>
#include <algorithm>
#include <string>
#include <set>

using namespace std;

int maxTandem(string& str){
for(int inteval = str.length()/2; inteval>=0; --inteval){
for(int i = 0 ; i <=str.length()-2*inteval; ++i){
bool flag = false;
for(int j = i,k=i+inteval; j < i+inteval; j++,k++){
if(str[j] != str[k]){
flag = true;
break;
}
}
if(!flag) return inteval;
}
}
return 0;
}

int main(){
string str;
int k;
cin  >> str >> k;
int len = str.length();
if(k>=len){
cout<<((k+len)%2 ? k+len-1:k+len)<<endl;
}else{
int newlen = len+k, startIndex=newlen-newlen/2*2, p =newlen/2;
for( p = newlen/2; p> k;  -- p){
int startIndex=newlen-p*2;
bool flag = false;
for(int i = startIndex, j = startIndex+p;  i < min(len,startIndex+p) && j < len; ++ i, ++ j){
if(str[i] != str[j]){
flag = true;
break;
}
}
if(!flag) break;
}
cout<<2*max(p,maxTandem(str))<<endl;
}
}

View Code
本题将上面两个部分合并，即在字符串s后面添加k个‘?’,再对整个字符串搜索

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>

using namespace std;

int main(){
string s;
int k;
cin >> s >> k;
int slen = s.length();
s+=string(k,'?');
int len = s.length()/2, interval = len;
for(interval = len; interval >=0; interval--){
bool flag = false;
for(int p = 0; p<= s.length()-2*interval; ++ p){
flag = false;
for(int i = p, j = p+interval; i < min(slen,p+interval) && j < slen; ++ i, ++ j){
if(s[j]!= '?' && s[i]!=s[j] ){ flag = true;break;}
}
if(!flag) break;
}
if(!flag) break;
}
cout<<2*interval<<endl;
}