Sudoku

Sudoku

Yi Sima was one of the best counselors of Cao Cao. He likes to play a funny game himself. It looks like the modern Sudoku, but smaller.  Actually, Yi Sima was playing it different. First of all, he tried to generate a board with every row contains 1 to 4, every column contains 1 to 4. Also he made sure that if we cut the board into four pieces, every piece contains 1 to 4.  Then, he removed several numbers from the board and gave it to another guy to recover it. As other counselors are not as smart as Yi Sima, Yi Sima always made sure that the board only has one way to recover.  Actually, you are seeing this because you've passed through to the Three-Kingdom Age. You can recover the board to make Yi Sima happy and be promoted. Go and do it!!! Input   The first line of the input gives the number of test cases,  .  test cases follow. Each test case starts with an empty line followed by 4 lines. Each line consist of 4 characters. Each character represents the number in the corresponding cell (one of '1', '2', '3', '4'). '*' represents that number was removed by Yi Sima.  It's guaranteed that there will be exactly one way to recover the board.   Output   For each test case, output one line containing  Case #x: , where  is the test case number (starting from 1). Then output 4 lines with 4 characters each. indicate the recovered board.   Sample Input 3 **** 2341 4123 3214 *243 *312 *421 *134 *41* **3* 2*41 4*2* Sample Output Case #1: 1432 2341 4123 3214 Case #2: 1243 4312 3421 2134 Case #3: 3412 1234 2341 4123

题意：每行每列都有1234，划分成4个2*2的小块，每个小块也有1234

思路：搜索+回溯

AC代码：

[cpp]  view plain  copy #include<iostream>  #include<cstdio>  #include<cstring>  #include<string>  #include<algorithm>  #include<cmath>  #include<utility>  #include<set>  #include<vector>  #include<map>  #include<queue>  #include<stack>  #define maxn 1010  #define INF 0x3f3f3f3f  #define LL long long  #define ULL unsigned long long  #define E 1e-8  #define mod 1000000007  #define P pair<int,int>  using namespace std;    struct node  {      int x,y;  }f[20];  int t;  char a[10][10];  int ans;  bool flag;  map<char,int>m;    /*bool check() {     for(int i=0;i<4;i++){         m.clear();         for(int j=0;j<4;j++){             if(m[a[i][j]]){                 return false;             }             m[a[i][j]]++;         }     }     for(int i=0;i<4;i++){         m.clear();         for(int j=0;j<4;j++){             if(m[a[j][i]]){                 return false;             }             m[a[j][i]]++;         }     }     for(int k=0;k<4;k++){         m.clear();         for(int i=(k/2)*2;i<(k/2)*2+2;i++){             for(int j=(k%2)*2;j<(k%2)*2+2;j++){                 if(m[a[i][j]]){                     return false;                 }                 m[a[i][j]]++;             }         }     } }*/    bool check(int x,int y,char s)  {      for(int i=0;i<4;i++){          if(a[x][i]==s) return false;          if(a[i][y]==s) return false;      }      for(int i=(x/2)*2;i<(x/2)*2+2;i++){          for(int j=(y/2)*2;j<(y/2)*2+2;j++){              if(a[i][j]==s) return false;          }      }      return true;  }    void dfs(int step)  {      if(step==ans){          for(int i=0;i<4;i++){              for(int j=0;j<4;j++){                  printf("%c",a[i][j]);              }              printf("\n");          }          flag=true;          return;      }      int x=f[step].x;      int y=f[step].y;      for(int i=1;i<=4&&!flag;i++){          char ss='0'+i;          if(check(x,y,ss)){              a[x][y]=ss;              //cout<<a[x][y]<<endl;              dfs(step+1);              a[x][y]='*';          }      }  }    int main()  {      scanf("%d",&t);      getchar();      int cas=0;      while(t--){          //    getchar();          ans=0;          for(int i=0;i<4;i++){              scanf("%s",a[i]);              for(int j=0;j<4;j++){                  if(a[i][j]=='*'){                      f[ans].x=i;                      f[ans++].y=j;                  }              }          }          flag=false;          printf("Case #%d:\n",++cas);          dfs(0);      }      return 0;  }