搜索/sgu 125 Shtirlits

题意

　　给出一个n*n的数组b，b[i,j]表示在数组a中，比a[i,j]大的上下左右一共有多少个

　　求一个满足b的a

分析

　　数据范围n<=4，很明显，深搜

　　对于每一个格子，从1~n*n枚举，在检查上一个合法之后，进行下一步的搜索

Accepted Code

 1 {

 2         PROBLEM：sgu125

 3         AUTHER：Rinyo

 4         MEMO：深搜 

 5 }

 6 Program sgu125;

 7 Const

 8   Infile = 'sgu125.in';

 9   Outfile = 'sgu125.out';

10   dx:Array[1..4]Of Longint=(-1,1,0,0);

11   dy:Array[1..4]Of Longint=(0,0,-1,1);

12 Var

13   a,b:Array[0..4,0..4]Of Longint;

14   n,i,j:Longint;

15   flag:Boolean;

16 Function check(x,y:Longint):Boolean;

17 Var

18   ans,i,xx,yy:Longint;

19 Begin

20   ans:=0;

21   For i:=1 To 4 Do Begin

22     xx:=x+dx[i];yy:=y+dy[i];

23     If a[xx,yy]>a[x,y] Then Inc(ans);

24   End;

25   If ans=b[x,y] Then check:=true Else check:=false;

26 End;

27 Procedure dfs(x,y:Longint);

28 Var

29   i,j:Longint;

30 Begin

31   If x=n+1 Then BEgin

32     For i:=1 To n Do

33       If not check(n,i) Then Exit;

34     flag:=true;

35     Exit;

36   End;

37   For i:=1 To n*n Do Begin

38     a[x,y]:=i;

39     If (x=1) Or check(x-1,y) Then Begin

40       If (y=n) Then dfs(x+1,1) Else dfs(x,y+1);

41       If flag Then Exit;

42     End;

43   End;

44 End;

45 Begin

46   Assign(input,infile);Reset(input);

47   Assign(output,outfile);Rewrite(output);

48   ReadLn(n);

49   For i:=1 To n Do Begin

50     For j:=1 To n Do Read(b[i,j]);

51     ReadLn;

52   End;

53   flag:=false;

54   dfs(1,1);

55   If not flag Then WriteLn('NO SOLUTION')

56               Else Begin

57                 For i:=1 To n Do Begin

58                   For j:=1 To n-1 Do Write(a[i,j],' ');

59                   WriteLn(a[i,n]);

60                 End;

61               ENd;

62   Close(input);Close(output);

63 End.