How many weighing do we need to perform in order to correctly identify the different egg?

Question

You have 19 eggs.
18 of them have the same weight and 1 of them is different,
but you do not know if it is heavier or lighter than the others.

Using the best possible strategy, in the worst case scenario,
how many weighing do we need to perform
in order to correctly identify the different egg?

Edit : You do not necessarily need to find if the egg is heavier or lighter than the others.

Answer 1

Group as- A= 6, B=6, C=6, D=1
Step 1. Weight A&B
Step 2. Weight A&C
If both equal, D is the different egg.
If one group is different - A, B or C then different egg can be found in 2 weightings in 2 ways
1. Make 3 groups of 2, weight 2+2 then 1+1 to find different egg
2. Make 2 groups of 3, weight 3+3, then 1+1 to find different egg