Do Not Touch the MEX!!!

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Utkarsh has a [permutation](https://en.wikipedia.org/wiki/Permutation) $P$ of $\{0, 1, 2, \dots, N-1\}$. He wants to find the number of pairs $(L, R)$ $(1 \leq L \lt R \leq N)$ such that swapping the elements $P_L$ and $P_R$ does not change the [MEX](https://en.wikipedia.org/wiki/Mex_(mathematics)) of any [subarray](https://stackoverflow.com/a/45686639). Formally, find the number of pairs $(L, R

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solution.cppC++17

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