Problem D: Dominos
Dominos are lots of fun. Children like to stand the tiles on their side
in long lines. When one domino falls, it knocks down the next one, which
knocks down the one after that, all the way down the line. However,
sometimes a domino fails to knock the next one down. In that case,
we have to knock it down by hand to get the dominos falling again.
Your task is to determine, given the layout of some domino tiles,
the minimum number of dominos that must be knocked down by hand in
order for all of the dominos to fall.
The first line of input contains one integer specifying the number of
test cases to follow. Each test case begins with a line containing
two integers, each no larger than 100 000. The first integer n is the number of domino tiles and the
second integer m is the number of lines to follow in the test case.
The domino tiles are numbered from 1 to n.
Each of the following lines contains two integers x and y
indicating that if domino number x falls, it will cause
domino number y to fall as well.
For each test case, output a line containing one integer, the minimum
number of dominos that must be knocked over by hand in order for
all the dominos to fall.
Output for Sample Input
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