算法学习【12】—— 1155. Can I Post the lette

题目来源：http://soj.me/1155

1155. Can I Post the lette

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

Problem Source

ZSUACM Team Member

思路：继续水……Washall算法应用……

代码：

#include <iostream>using namespace std;bool map[200][200];int main(){int cityNum;int roadNum;int i,j,k;while (cin >> cityNum && cityNum != 0){cin >> roadNum;for(i = 0; i < cityNum; i++){for(j = 0; j < cityNum; j++){map[i][j] = false;}}while(roadNum--){cin >> i >> j;map[i][j] = true;}for(i = 0; i < cityNum; i++){for(j = 0; j < cityNum; j++){if(map[i][j]){for(k = 0; k < cityNum; k++){if(map[j][k]){map[i][k] = true;}}}}}if(map[0][cityNum - 1]){cout << "I can post the letter\n";}else{cout << "I can't post the letter\n";}}return 0;}