PAT/html/t1008.html

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<h1>1008. Airline Routes (35)</h1>
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<p>Given a map of airline routes, you are supposed to check if a round trip can be planned between any pair of cities.</p>
<p><b>
Input Specification:
</b></p>
<p>Each input file contains one test case.  For each case, the first line gives two positive integers N (2&lt;= N &lt;= 10<sup>4</sup>) and M (&lt;=6N), which are the total number of cities (hence the cities are numbered from 1 to N) and the number of airline routes, respectively.  Then M lines follow, each gives the information of a route in the format of the source city index first, and then the destination city index, separated by a space.  It is guaranteed that the source is never the same as the destination.</p>
<p>After the map information, another positive integer K is given, which is the number of queries.  Then K lines of queries follow, each contains a pair of distinct cities' indices.</p>
<p><b>
Output Specification:
</b></p>
<p>For each query, output in a line "Yes" if a round trip is possible, or "No" if not.</p>
<b>Sample Input:</b><pre>
12 19
3 4
1 3
12 11
5 9
6 2
3 2
10 7
9 1
7 12
2 4
9 5
2 6
12 4
11 10
4 8
8 12
11 8
12 7
1 5
20
11 4
12 7
3 6
2 3
5 3
3 9
4 3
8 3
8 10
10 11
7 8
7 1
9 5
1 9
2 6
3 1
3 12
7 3
6 9
6 8
</pre>
<b>Sample Output:</b><pre>
Yes
Yes
No
No
No
No
No
No
Yes
Yes
Yes
No
Yes
Yes
Yes
No
No
No
No
No
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