Handling Edge Cases

Watch out for these edge cases:

$1.$ Empty input: : Return $0$ (or appropriate default).

$2.$ Single interval: : Return $1$.

$3.$ Ties in end time: : If two activities end at the same time, the order between them does not matter. Both are valid greedy choices.

$4.$ Touching intervals: : $[1,2]$ and $[2,3]$ do not overlap. They share a point but can both be selected. Always check the problem statement for whether touching intervals overlap. Common bug: using < instead of <= for overlap check.