拼图——dfs

题目链接：https://www.luogu.com.cn/problem/P3969

分析等会再补，先贴代码。

代码：

#include<iostream>
#include<cstdio>
#include<cstring>
#include<cmath>
#include<queue>
using namespace std;
#define int long long
#define debug printf("zjyvegetable
")
inline int read(){
    int a=0,b=1;char c=getchar();
    while(!isdigit(c)){if(c=='-')b=-1;c=getchar();}
    while(isdigit(c)){a=a*10+c-'0';c=getchar();}
    return a*b;
}
const int N=20;
int n,r[N],c[N],s[N][5][5],t[5][5],ans,a[5][5],pre[N],rem;
char cc[N];
bool check(int p,int x,int y){
    if(x+r[p]-1>4||y+c[p]-1>4)return false;
    for(int i=x;i<=x+r[p]-1;i++){
        for(int j=y;j<=y+c[p]-1;j++)
        if(s[p][i-x+1][j-y+1]&&t[i][j])return false;
    }
    return true;
}
void putin(int p,int x,int y){
    for(int i=x;i<=x+r[p]-1;i++){
        for(int j=y;j<=y+c[p]-1;j++){
            if(s[p][i-x+1][j-y+1])t[i][j]=s[p][i-x+1][j-y+1];
        }
    }
}
void takeout(int p,int x,int y){
    for(int i=x;i<=x+r[p]-1;i++){
        for(int j=y;j<=y+c[p]-1;j++)
        if(s[p][i-x+1][j-y+1])t[i][j]=0;
    }
}
bool jud(){
    for(int i=1;i<=4;i++){
        for(int j=1;j<=4;j++){
            if(!t[i][j])return false;
        }
    }
    return true;
}
void dfs(int p){
    //printf("%lld
",p);
    if(pre[p]){
        dfs(p+1);return;
    }
    if(jud()){
        ans++;
        if(ans==2)rem=1;
        if(ans==1){
            for(int i=1;i<=4;i++){
                for(int j=1;j<=4;j++){
                    a[i][j]=t[i][j];
                }
            }
        }
        return;
    }
    if(p==n+1)return;
    for(int i=1;i<=4;i++){
        for(int j=1;j<=4;j++){
            if(!check(p,i,j))continue;
            putin(p,i,j);
            dfs(p+1);
            if(rem)return;
            takeout(p,i,j);
        }
    }
    dfs(p+1);
}
signed main(){
    while(scanf("%lld",&n)!=EOF){
        memset(t,0,sizeof(t));
        memset(pre,0,sizeof(pre));
        for(int i=1;i<=n;i++){
            r[i]=read();c[i]=read();
            if(r[i]>4||c[i]>4)pre[i]=1;
            for(int j=1;j<=r[i];j++){
                scanf("%s",cc);
                for(int k=1;k<=c[i];k++){
                    s[i][j][k]=(cc[k-1]-'0'==1?i:0);
                }
            }
        }
        ans=0;rem=0;
        dfs(1);
        if(!ans){
            printf("No solution
");
        }
        else if(ans>1){
            printf("Yes, many!
");
        }
        else{
            printf("Yes, only one!
");
            for(int i=1;i<=4;i++){
                for(int j=1;j<=4;j++)
                printf("%lld",a[i][j]);
                printf("
");
            }
        }
    }
    return 0;
}