ACM-搜索之Robot Motion——hdu1035

Robot Motion

题目：http://acm.hdu.edu.cn/showproblem.php?pid=1035

Problem 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

Sample Output
10 step(s) to exit

3 step(s) before a loop of 8 step(s)

深搜中的一道题，这题目不需要你来行走，地图会告诉你该怎么走，你只需要判断：

1.是否能走出来，走出来则要走几步。

2.走不出来会转圈，从入口到转圈几步，这个圈有几步。

入口是从第一行进去，它只会给你纵坐标。

我的方法是：递归套，两个判断，先判断是否能走出来，再判断该点与之前的点是否有相同的（即判断是否转圈）

剩下的好做了。

代码：

// robot motion
#include <iostream>
using namespace std;

char dt[1001][1001];
int n,m,loop,out,loop_pt;
struct Coordinate
{
    int x,y;
}path[1001];
// iswt为1则代表转圈，为2则代表出来了
int iswt;

void dfs(int xx,int yy,int num)
{
    if(iswt==1 || iswt==2)  return;
    // 查看是否已经走出来了
    if(xx==0 || yy==0 || xx==n+1 || yy==m+1)
    {
        out=num;
        iswt=2;
        return;
    }

    int i;
    // 查看这个点是否曾经走过
    for(i=0;i<num;++i)
        if(xx==path[i].x && yy==path[i].y)
        {
            loop=num-i;
            loop_pt=i;
            iswt=1;
            return;
        }

    // 记录当前路径，并根据地图上的内容向相应方向移动
    path[num].x=xx,path[num].y=yy;
    if(dt[xx][yy]=='N') dfs(xx-1,yy,num+1);
    else if(dt[xx][yy]=='S')    dfs(xx+1,yy,num+1);
    else if(dt[xx][yy]=='E')    dfs(xx,yy+1,num+1);
    else    dfs(xx,yy-1,num+1);
}

int main()
{
    int start,i,j;
    while(cin>>n>>m)
    {
        if(n==0 && m==0)    break;

        cin>>start;
        for(i=1;i<=n;++i)
            for(j=1;j<=m;++j)
                cin>>dt[i][j];

        iswt=0;
        dfs(1,start,0);

        if(iswt==2)
            cout<<out<<" step(s) to exit"<<endl;
        else if(iswt==1)
            cout<<loop_pt<<" step(s) before a loop of "<<loop<<" step(s)"<<endl;
    }
    return 0;
}