Second Largest Number in O(1) Time and Space using JavaScript

Input: A = 7, B = 3, C = 9
Output: 7

Input: A = 12, B = 8, C = 3
Output: 8

There are three candidates to the solution: A, B and C. We should try out each of them until we find the correct one. How can we check if A is the solution? What should happen for A to be the second largest value?

A is the second largest value if the smaller of B and C is less than or equal to A, and A is less than or equal to the larger of B and C. We can write an if statement checking these two conditions and, if they hold, return A. What if the conditions don't hold and A is not the solution? What should we do next?

We should test B. Similarly, B is the second largest value if the smaller of A and C is less than or equal to B, and B is less than or equal to the larger of A and C. We can write a second if statement checking these conditions and, if they hold, return B. What if not even B is the solution?

Then, it's clear that C is the solution, so we should return C. We don't even need to check the conditions anymore.