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

本題要考慮字串本身就存在tandem，

如測試用例

aaaaaaaaabbb

3

輸出結果應該是8而不是6，因為字串本身的tanderm時最長的

故要考慮字串本身的最大的tanderm和新增k個字元後最大的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;
    }
}

 本題將上面兩個部分合並，即在字串s後面新增k個‘?’,再對整個字串搜尋

#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;
}