luogu_1092 虫食算

#include <iostream>
#include <cstring>
#include <cstdio>
using namespace std;
const int N=30;
int n,s1[4][N],num[N];
char s[4][N];
bool vis[N];

void dfs(int x,int y,int t){
    if(x==0){
        if(t==0){
            for(int i=1;i<=n;i++)printf("%d ",num[i]);
            puts("");
            exit(0);
        }
        return;
    }
    for(int i=x-1;i>=1;i--){
        int w1=num[s1[1][i]],w2=num[s1[2][i]],w3=num[s1[3][i]];
        if(w1==-1 || w2==-1 || w3==-1)continue;
        if((w1+w2)%n!=w3 && (w1+w2+1)%n!=w3)return;
    }
    if(num[s1[y][x]]==-1){
        for(int i=n-1;i>=0;i--){
            if(!vis[i]){
                if(y!=3){
                    num[s1[y][x]]=i;
                    vis[i]=1;
                    dfs(x,y+1,t);
                    num[s1[y][x]]=-1;
                    vis[i]=0;
                }
                else{
                    int w=num[s1[1][x]]+num[s1[2][x]]+t;
                    if(w%n!=i)continue;
                    vis[i]=1;
                    num[s1[3][x]]=i;
                    dfs(x-1,1,w/n);
                    vis[i]=0;
                    num[s1[3][x]]=-1;
                }
            }
        }
    }
    else {
        if(y!=3)dfs(x,y+1,t);
        else {
            int w=num[s1[1][x]]+num[s1[2][x]]+t;
            if(w%n!=num[s1[3][x]])return;
            dfs(x-1,1,w/n);
        }
    }
}

int main(){
    scanf("%d",&n);
    for(int i=1;i<=3;i++)scanf("%s",s[i]+1);
    for(int i=1;i<=n;i++)s1[1][i]=s[1][i]-‘A‘+1;
    for(int i=1;i<=n;i++)s1[2][i]=s[2][i]-‘A‘+1;
    for(int i=1;i<=n;i++)s1[3][i]=s[3][i]-‘A‘+1;
    memset(num,0xff,sizeof(num));
    memset(vis,0,sizeof(vis));
    dfs(n,1,0);
    return 0;
}