POJ 3923 - 模拟，要细心

<ACM国际大学生程序设计竞赛亚洲区域真题题解>上的一题...模拟水过...不过一定要留意特殊情况..WA了两次.......discuss里有给出 ...考虑问题要全面...

Program：

#include<iostream>#include<stdio.h>#include<algorithm>#include<string.h>#include<math.h>#include<map>#include<queue>#include<stack>#define ll long long#define oo 1000000000#define pi acos(-1)using namespace std;int w,h,move[4][2]={{0,1},{1,0},{0,-1},{-1,0}};char arc[105][105];bool ok(char c){     int y,x,yy,xx,i,j,k;     for (y=1;y<=h;y++)        for (x=1;x<=w;x++)           if (arc[y][x]==c) goto A;     A: ;     if (y>h) return false;     k=0;     if (arc[move[k][0]+y][move[k][1]+x]!=c) k++;     k%=4;     j=y+move[k][0]; i=x+move[k][1];       while (x!=i || y!=j)     {            if (arc[j][i]!=c) return false;            if (arc[move[k][0]+j][move[k][1]+i]!=c)             {                   k++;                   if (k==2)                    {                        yy=j;                        xx=i;                   }            }            k%=4;            j=j+move[k][0];  i=i+move[k][1];     }     for (i=y+1;i<yy;i++)        for (j=x+1;j<xx;j++)           if (arc[i][j]!='.') return false;     return true;}int main(){       int i,j;     char c;     while (~scanf("%d%d",&h,&w))     {             if (!h && !w) break;             for (i=0;i<=h+1;i++) arc[i][0]=arc[i][w+1]='?';             for (i=0;i<=w+1;i++) arc[0][i]=arc[h+1][i]='?';             for (i=1;i<=h;i++) scanf("%s",arc[i]+1);             for (c='A';c<='Z';c++)                 if (ok(c)) printf("%c",c);             printf("\n");     }     return 0;}