POJ 1573 Robot Motion

Robot Motion

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 8130 Accepted: 3929

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 5NEESWEWWWESSSNWWWW4 5 1SESWEEESNWNWEENEWSEN0 0 0

Sample Output

10 step(s) to exit3 step(s) before a loop of 8 step(s)

Source

Mid-Central USA 1999

解题思路：模拟题总体还是属于简单题，这一题用一个数组保存该点距出发点的距离，一个step记录走的步数，若是之前已访问过该点，就是循环，输出该点距出发点的距离再输出步数减距离再加1就是循环了多少次，否则直接输出步数减1.

#include<iostream>using namespace std;char maze[15][15];int visit[15][15],loop,step,p,q;bool v[15][15];bool Solve(int x,int y){loop=0;step=-1;//因为第一步不用走，就是开始是0，所以步数初始化为-1do{    if(maze[x][y]=='*')    return 1;switch(maze[x][y])//每次对即将走的一步判断是否构成循环{case 'E':if(v[x][y])     {loop=step-visit[x][y];p=x;q=y;return 0;}step++;visit[x][y]=step;v[x][y]=true;y++;break;case 'W':if(v[x][y])     {loop=step-visit[x][y];p=x;q=y;return 0;}step++;visit[x][y]=step;v[x][y]=true;y--;break;case 'N':if(v[x][y])     {loop=step-visit[x][y];p=x;q=y;return 0;}step++;visit[x][y]=step;v[x][y]=true;x--;break;case 'S':if(v[x][y])     {loop=step-visit[x][y];p=x;q=y;return 0;}step++;visit[x][y]=step;v[x][y]=true;x++;break;}}while(1);}int main(){int i,j,m,n,pos;while(cin>>m>>n>>pos&&(m||n||pos)){memset(maze,'*',sizeof(maze));memset(v,false,sizeof(v));for(i=0;i<15;i++)for(j=0;j<15;j++)visit[i][j]=1;for(i=1;i<=m;i++)for(j=1;j<=n;j++)cin>>maze[i][j];if(Solve(1,pos))cout<<step+1<<" step(s) to exit"<<endl;//想走出迷宫还要在出口处多走一步elsecout<<visit[p][q]<<" step(s) before a loop of "<<loop+1<<" step(s)"<<endl;//loop是未闭合的环的步数，所以再加1}}