Robot Motion(模拟法)

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Robot Motion

Time Limit: 1000MS Memory Limit: 10000KTotal Submissions: 13093 Accepted: 6342

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

题意：给出3个数字，分别为指令矩阵的行数、列数和机器人进入矩阵时所在列。机器人每次都从矩阵的北边进入矩阵，矩阵中的字符指代机器人的移动方向，输出机器人在矩阵中的移动步数；如果机器人进入死循环，输出进入死循环前的移动步数和死循环的大小。 
分析：模拟机器人在矩阵走，如果某个方格经过了两次，说明进入了死循环

#include <iostream>#include <cstdio>#include <cstring>using namespace std;int main(){    int n,m,s,i,j,k;    int v[20][20];    char a[20][20];    while(scanf("%d%d%d",&n,&m,&s)!=EOF)    {          if(n==0&&m==0&&s==0)            break;          memset(v,0,sizeof(v));          for(i=1;i<=n;i++)            for(j=1;j<=m;j++)          {             cin>>a[i][j];          }          i=1;j=s;k=0;          int flag=1;          while(i>=1&&i<=n&&j<=m&&j>=1)          {     k++;                if(v[i][j])//已走过一次再走到这儿便是循环                {                   flag=0;                   break;                }                else                {                    v[i][j]=k;                    if(a[i][j]=='N')                        i--;                    else if(a[i][j]=='E')                        j++;                    else if(a[i][j]=='S')                        i++;                    else if(a[i][j]=='W')                        j--;                }          }          if(flag==1)            cout<<k<<" step(s) to exit"<<endl;          else            cout<<v[i][j]-1<<" step(s) before a loop of "<<k-v[i][j]<<" step(s)"<<endl;//走入死循环前的步数第一圈死循环不算步数   一圈死循环所需的步数    }    return 0;}