When to Use Binary Search

Use binary search on answer when:

$1.$ The answer lies in a bounded numeric range

$2.$ You can write a feasibility function that returns true/false for a candidate answer

$3.$ The feasibility function is monotonic. If answer $x$ works, then either all $y > x$ work or all $y < x$ work

The pattern: binary search finds the boundary between feasible and infeasible. Your job is identifying what "feasible" means for each problem.