Editorial for GlobeX Cup '18 S1 - Code Copiers

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Author: Ninjaclasher

We can use a boolean array $k$ ~k~ to store whether there is a coder who this coder copies from. An element $i$ ~i~ in the array is $True$ ~True~ if coder $i$ ~i~ is not a source.

For all $i$ ~i~, we set $k_{a_i} = \text{True}$ ~k_{a_i} = \text{True}~, meaning that coder $a_i$ ~a_i~ is not a source.

Then, we can loop through the boolean array and count the number of $\text{False}$ ~\text{False}~ elements.

Time Complexity: $\mathcal{O}(N)$ ~\mathcal{O}(N)~

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