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Solution: Nth Magical Number

Understand how to find the nth magical number divisible by either a or b by applying inclusion-exclusion to count candidates and using binary search to identify the correct number efficiently. This lesson helps you grasp the mathematical and algorithmic techniques involved, including computing least common multiples and managing large results with modular arithmetic.

Statement

Given three integers n, a, and b, return the nth magical number.

A magical number is defined as a positive integer that is divisible by either a or b.

As the result may be very large, return it modulo 109+710^9+7.

Constraints:

  • 11 \leq n 109\leq 10^9

  • ...