MEX-OR

The *MEX* (minimum excluded) of an array is the smallest non-negative integer that does not belong to the array. For instance: - The MEX of $[2, 2, 1]$ is $0$, because $0$ does not belong to the array. - The MEX of $[3, 1, 0, 1]$ is $2$, because $0$ and $1$ belong to the array, but $2$ does not. - The MEX of $[0, 3, 1, 2]$ is 4 because $0, 1, 2$ and $3$ belong to the array, but $4$ does not. Fin