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 $True$ $T r u e$ if coder $i$ $i$ is not a source.

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

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

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

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