POJ_1573 Robot Motion

问题来源:http://poj.org/problem?id=1573

Robot Motion
Time Limit: 1000MS  Memory Limit: 10000K
Total Submissions: 7083  Accepted: 3402

Description



A robot has been programmed to follow the instructions in its path. Instructions for the next direction the robot is to move are laid down in a grid. The possible instructions are

N north (up the page)
S south (down the page)
E east (to the right on the page)
W west (to the left on the page)

For example, suppose the robot starts on the north (top) side of Grid 1 and starts south (down). The path the robot follows is shown. The robot goes through 10 instructions in the grid before leaving the grid.

Compare what happens in Grid 2: the robot goes through 3 instructions only once, and then starts a loop through 8 instructions, and never exits.

You are to write a program that determines how long it takes a robot to get out of the grid or how the robot loops around.

Input

There will be one or more grids for robots to navigate. The data for each is in the following form. On the first line are three integers separated by blanks: the number of rows in the grid, the number of columns in the grid, and the number of the column in which the robot enters from the north. The possible entry columns are numbered starting with one at the left. Then come the rows of the direction instructions. Each grid will have at least one and at most 10 rows and columns of instructions. The lines of instructions contain only the characters N, S, E, or W with no blanks. The end of input is indicated by a row containing 0 0 0.
Output

For each grid in the input there is one line of output. Either the robot follows a certain number of instructions and exits the grid on any one the four sides or else the robot follows the instructions on a certain number of locations once, and then the instructions on some number of locations repeatedly. The sample input below corresponds to the two grids above and illustrates the two forms of output. The word "step" is always immediately followed by "(s)" whether or not the number before it is 1.
Sample Input

3 6 5
NEESWE
WWWESS
SNWWWW
4 5 1
SESWE
EESNW
NWEEN
EWSEN
0 0 0
Sample Output

10 step(s) to exit
3 step(s) before a loop of 8 step(s)


题目大意:模拟一个机器人在特定的棋盘中行走，每个棋盘的格子规定好了机器人移动的方向，每次移动只能走一个格子，问机器人退出棋盘时走的步数，如果不能退出棋盘，输出机器人进入循环前走的步数和每次循环中包含的步数。

分析：简单模拟题，注意第二种情况，即发生循环的时候如何得到循环前的步数，这里想到用父指针。

代码：

#include<stdio.h>
#include<string.h>
#define SIZE 12

typedef int point[2];
point father[SIZE][SIZE];
int state[SIZE][SIZE];
char maze[SIZE][SIZE];
int R,C,S;

void solve(int r,int c,int lr,int lc,int dis)
{
    if(r<=0||r>R||c<=0||c>C)
    {
        printf("%d step(s) to exit\n",dis-1);
        return;
    }
    if(state[r][c]!=0)
    {
        printf("%d step(s) before a loop of %d step(s)\n",state[father[r][c][0]][father[r][c][1]],dis-state[father[r][c][0]][father[r][c][1]]-1);
        return;
    }
    father[r][c][0] = lr;
    father[r][c][1] = lc;
    state[r][c] = dis;
    switch(maze[r][c])
    {
    case 'N':solve(r-1,c,r,c,dis+1);break;
    case 'S':solve(r+1,c,r,c,dis+1);break;
    case 'E':solve(r,c+1,r,c,dis+1);break;
    case 'W':solve(r,c-1,r,c,dis+1);break;
    }
    return;
}

int main()
{
    //freopen("datain.txt","r",stdin);
    //freopen("dataout.txt","w",stdout);
    while(scanf("%d%d%d%*c",&R,&C,&S),R||C||S)
    {
        for(int i=1;i<=R;i++)
        gets(maze[i]);
        memset(state,0,sizeof(state));
        for(int i=1;i<=R;i++)
        {
            for(int j=C;j>0;j--)
            {
                maze[i][j] = maze[i][j-1];
            }
        }

        solve(1,S,0,S,1);
    }
    return 0;
}