poj2488(dfs)

#include<stdio.h>
#include<string.h>

char x[26],y[26];
bool visit[26][26];
int map[26][26];
int dx[]={-1,1,-2,2,-2,2,-1,1};
int dy[]={-2,-2,-1,-1,1,1,2,2};
int sum;
int flag;
int p,q;

void dfs(int xx,int yy,int step)
{
    if(step==sum)
    {
        for(int i=0;i<step;i++)
        {
            printf("%c%c",y[i],x[i]);
        }
        flag=1;
        printf("\n\n");

        return;
    }

    if(flag) return;

    for(int i=0;i<8;i++)
    {
        int nx=xx+dx[i];
        int ny=yy+dy[i];

        if(nx>0&&ny>0&&nx<=p&&ny<=q&&!visit[nx][ny])
        {
            x[step]='1'+nx-1;
            y[step]='A'+ny-1;

            visit[nx][ny]=1;
            dfs(nx,ny,step+1);
            visit[nx][ny]=0;

        }
    }
}
int main()
{
    int n,i;
    int t;

    int ase=0;

    scanf("%d",&t);

    while(t--)
    {

        scanf("%d%d",&p,&q);

         ase++;
         flag=0;
        printf("Scenario #%d:\n",ase);
        memset(visit,0,sizeof(visit));


        sum=p*q;

        visit[1][1] = 1;
        x[0]='1';
        y[0]='A';

        dfs(1,1,1);
        if(!flag) printf("impossible\n\n");


    }
    return 0;
}

A Knight's Journey

Time Limit: 1000MS		Memory Limit: 65536K
Total Submissions: 41217		Accepted: 14025

Description

Background
The knight is getting bored of seeing the same black and white squares again and again and has decided to make a journey
around the world. Whenever a knight moves, it is two squares in one direction and one square perpendicular to this. The world of a knight is the chessboard he is living on. Our knight lives on a chessboard that has a smaller area than a regular 8 * 8 board, but it is still rectangular. Can you help this adventurous knight to make travel plans?

Problem
Find a path such that the knight visits every square once. The knight can start and end on any square of the board.

Input

The input begins with a positive integer n in the first line. The following lines contain n test cases. Each test case consists of a single line with two positive integers p and q, such that 1 <= p * q <= 26. This represents a p * q chessboard, where p describes how many different square numbers 1, . . . , p exist, q describes how many different square letters exist. These are the first q letters of the Latin alphabet: A, . . .

Output

The output for every scenario begins with a line containing "Scenario #i:", where i is the number of the scenario starting at 1. Then print a single line containing the lexicographically first path that visits all squares of the chessboard with knight moves followed by an empty line. The path should be given on a single line by concatenating the names of the visited squares. Each square name consists of a capital letter followed by a number.
If no such path exist, you should output impossible on a single line.

Sample Input

3
1 1
2 3
4 3

Sample Output

Scenario #1:
A1

Scenario #2:
impossible

Scenario #3:
A1B3C1A2B4C2A3B1C3A4B2C4

Source