http://poj.org/problem?id=2488
DFS+回溯，其实不用从所有节点开始搜索，因为要求输出的是字典序，所以只从A1开始搜索，能一次搜到便是存在，否则不存在。写完代码才意识到。另外注意字典序时，方向数组要写对。
1 #include <stdio.h> 2 #include <stdlib.h> 3 #include <string.h> 4 #include <stack> 5 using namespace std; 6 int c; 7 int n,p,q; 8 int start_x,start_y; 9 int total_count=0; 10 bool flag=false; 11 bool visited[30][30]={false}; 12 typedef struct Node { 13 int x,y; 14 }Node; 15 Node nodes[8]={{-2,-1},{-2,1},{-1,-2},{-1,2},{1,-2},{1,2},{2,-1},{2,1}}; 16 typedef struct Father { 17 int x,y; 18 }Father; 19 Father father[30][30]={{-1,-1}}; 20 void init() 21 { 22 flag=false; 23 memset(visited,false,sizeof(visited)); 24 } 25 bool check(int x,int y) 26 { 27 if(!(0<=x&&x<p&&0<=y&&y<q)) return false; 28 return true; 29 } 30 void out_result(int a,int b) 31 { 32 stack<int> S; 33 int x=a,y=b; 34 printf("Scenario #%d:\n",c); 35 S.push(b); 36 S.push(a); 37 while(!(father[x][y].x==-1&&father[x][y].y==-1)) { 38 S.push(father[x][y].y); 39 S.push(father[x][y].x); 40 int X=father[x][y].x,Y=father[x][y].y; 41 x=X; 42 y=Y; 43 } 44 while(!S.empty()) { 45 putchar(S.top()+'A'); 46 S.pop(); 47 putchar(S.top()+'1'); 48 S.pop(); 49 } 50 putchar('\n'); 51 putchar('\n'); 52 } 53 void dfs(int x,int y,int count) 54 { 55 if(flag) return; 56 if(count==total_count) { 57 out_result(x,y); 58 flag=true; 59 return ; 60 } 61 int i; 62 for(i=0;i<8;i++) { 63 if(check(x+nodes[i].x,y+nodes[i].y)&&!visited[x+nodes[i].x][y+nodes[i].y]) { 64 visited[x+nodes[i].x][y+nodes[i].y]=true; 65 father[x+nodes[i].x][y+nodes[i].y].x=x; 66 father[x+nodes[i].x][y+nodes[i].y].y=y; 67 dfs(x+nodes[i].x,y+nodes[i].y,count+1); 68 visited[x+nodes[i].x][y+nodes[i].y]=false; 69 } 70 } 71 } 72 int main() 73 { 74 scanf("%d",&n); 75 for(c=1;c<=n;c++) { 76 here: scanf("%d%d",&q,&p); 77 int i,j; 78 total_count=p*q; 79 for(i=0;i<p;i++) { 80 for(j=0;j<q;j++) { 81 visited[i][j]=true; 82 father[i][j].x=-1; 83 father[i][j].y=-1; 84 start_x=i; 85 start_y=j; 86 dfs(start_x,start_y,1); 87 if(flag) { 88 init(); 89 c++; 90 if(c<=n) 91 goto here; 92 else return 0; 93 } 94 init(); 95 } 96 } 97 if(!flag) { 98 printf("Scenario #%d:\n",c); 99 printf("impossible\n"); 100 putchar('\n'); 101 } 102 } 103 return 0; 104 }