sicily 1155 Can I Post the letter

Description

I am a traveler. I want to post a letter to Merlin. But because there are so many roads I can walk through, and maybe I can’t go to Merlin’s house following these roads, I must judge
whether I can post the letter to Merlin before starting my travel.

Suppose the cities are numbered from 0 to N-1, I am at city 0, and Merlin is at city N-1. And there are M roads I can walk through, each of which connects two cities. Please note that
each road is direct, i.e. a road from A to B does not indicate a road from B to A.

Please help me to find out whether I could go to Merlin’s house or not.

Input

There are multiple input cases. For one case, first are two lines of two integers N and M, (N<=200, M<=N*N/2), that means the number of citys and the number of roads. And Merlin stands
at city N-1. After that, there are M lines. Each line contains two integers i and j, what means that there is a road from city i to city j.

The input is terminated by N=0.

Output

For each test case, if I can post the letter print “I can post the letter” in one line, otherwise print “I can't post the letter”.

Sample Input

320 11 2310 10

Sample Output

I can post the letterI can't post the letter

简单的深搜

#include <iostream>

#include <stack>

using namespace std;

stack<int> st;

int load[200][200];

int isv[200][200];

int N;

bool cal(int a)

{

for(int i=0;i<N;i++)

{

if(load[a][i]==1&&isv[a][i]==0)

{

st.push(i);

}

while(!st.empty())

{

int k=st.top();

if(k==(N-1))

{

return true;

}

st.pop();

isv[a][i]=1;

cal(k);

}

}

return false;

}

int main()

{

while(cin>>N&&N!=0)

{

while(!st.empty())

{

st.pop();

}

for(int i=0;i<200;i++)

{

for(int j=0;j<200;j++)

{

load[i][j]=0;

isv[i][j]=0;

}

}

int M;

cin>>M;

for(int i=0;i<M;i++)

{

int a,b;

cin>>a;

cin>>b;

load[a][b]=1;

}

if(cal(0))

cout<<"I can post the letter"<<endl;

else

cout<<"I can't post the letter"<<endl;

}

return 0;

}