Rikka with string

Time Limit: 2000/1000 MS (Java/Others)    Memory Limit: 65536/65536 K (Java/Others)
Total Submission(s): 1411    Accepted Submission(s): 502

Problem Description

As
we know, Rikka is poor at math. Yuta is worrying about this situation,
so he gives Rikka some math tasks to practice. There is one of them:

One
day, Yuta got a string which contains n letters but Rikka
lost it in accident. Now they want to recover the string. Yuta remembers
that the string only contains lowercase letters and it is not a
palindrome string. Unfortunately he cannot remember some letters. Can
you help him recover the string?

It is too difficult for Rikka. Can you help her?

Input

This problem has multi test cases (no more than 20). For each test case, The first line contains a number n(1≤n≤1000). The next line contains an n-length string which only contains lowercase letters and ‘?’ – the place which Yuta is not sure.

Output

For
each test cases print a n-length string – the string you come up with.
In the case where more than one string exists, print the
lexicographically first one. In the case where no such string
exists, output “QwQ”.

Sample Input

5
a?bb?
3
aaa

Sample Output

aabba
QwQ

暴力:直接枚举?处的答案,得到的第一个必定字典序最小

#include<iostream>
#include<stdio.h>
#include<string.h>
#include<math.h>
#include <algorithm>
#include <map>
#include <vector>
using namespace std;
typedef long long LL;
char str[2005],res[2005];
int n;
bool flag;
bool judge(char *str){
    int len = strlen(str);
    for(int i=0,j=len-1;i<=j;i++,j--){
        if(str[i]!=str[j]) return true;
    }
    return false;
}
void dfs(int step){
    if(flag) return;
    if(step==n) {
        if(judge(str)){
            flag = true;
            strcpy(res,str);
        }
        return;
    }
    if(str[step]==‘?‘){
        for(int i=‘a‘;i<=‘z‘;i++){
            str[step]=i;
            dfs(step+1);
            str[step]=‘?‘;
        }
    }else{
        dfs(step+1);
    }
    return;
}
int main(){

    while(scanf("%d",&n)!=EOF){
        flag= false;
        scanf("%s",str);
        dfs(0);
        if(flag) printf("%s\n",res);
        else printf("QwQ\n");
    }
}