UVa: 10009 (All Roads Lead Where?)



// http://uva.onlinejudge.org/external/100/10009.html
// Runtime: 0.008s
// Tag: BFS 

// @BEGIN_OF_SOURCE_CODE

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <string>
#include <cctype>
#include <stack>
#include <queue>
#include <list>
#include <vector>
#include <map>
#include <sstream>
#include <cmath>
#include <bitset>
#include <utility>
#include <set>
#include <numeric>
#include <ctime>

#define Inf 2147483647
#define Pi acos(-1.0)
#define N 1000000
#define LL long long

inline LL Power(int b, int p) { LL ret = 1; for ( int i = 1; i <= p; i++ ) ret *= b; return ret; }
const int dr [] = {-1, -1, 0, 1, 1, 1, 0, -1};
const int dc [] = {0, 1, 1, 1, 0, -1, -1, -1};

#define F(i, a, b) for( int i = (a); i < (b); i++ )
#define Fs(i, sz) for( size_t i = 0; i < sz.size (); i++ )
#define Fe(i, x) for(typeof (x.begin()) i = x.begin(); i != x.end (); i++)
#define Set(a, s) memset(a, s, sizeof (a))
#define max(a, b)  (a < b ? b : a)
#define min(a, b)  (a > b ? b : a)

using namespace std;

int parentCity [26 + 5];
bool matrix [26 + 5] [26 + 5];

int main ()
{
	//freopen("input.txt", "r", stdin);
	//freopen("output.txt", "w", stdout);

	int testCases; scanf ("%d", &testCases);
	bool blank = false;

	while ( testCases-- ) {
		int city;
		int query;
		scanf ("%d %d", &city, &query);

		// clean up
		Set(matrix, false);

		char city1 [100];
		char city2 [100];
		for ( int i = 0; i < city; i++ ) {
			scanf ("%s %s", city1, city2);
			// roads are bi-directional 
			matrix [city1 [0] - 'A'] [city2 [0] - 'A'] = matrix [city2 [0] - 'A'] [city1 [0] - 'A'] = true;
		}

		if ( blank ) printf ("\n");
		blank = true;

		for ( int i = 0; i < query; i++ ) {
			scanf ("%s %s", city1, city2);
			queue <int> q;
			q.push(city1 [0] - 'A');
			Set(parentCity, -1);
			// source is a parent of itself 
			parentCity [city1 [0] - 'A'] = city1 [0] - 'A';

			while ( !q.empty() ) {
				int popCity = q.front();
				q.pop();

                // we found the destination city 
				if (popCity == city2 [0] - 'A') break;

				for ( int j = 0; j < 26; j++ ) {
					if ( matrix [popCity] [j] && parentCity [j] == -1 ) {
						parentCity [j] = popCity;
						q.push(j);
					}
				}
			}

			// format the output
			stack <char> output;
			int cityIterator = city2 [0] - 'A';
			output.push(city2 [0]);

            // traverse back to build the path 
			while ( parentCity [cityIterator] != cityIterator ) {
				output.push(parentCity [cityIterator] + 'A');
				cityIterator = parentCity [cityIterator];
			}

			// print output
			while ( !output.empty() ) { printf ("%c", output.top()); output.pop(); }
			printf ("\n");
		}
	}

	return 0;
}

// @END_OF_SOURCE_CODE
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