Solve The Equation

Chef has an array $A_1, A_2........A_N$ of size $N$ and a number $M$. He is very much interested in an equation, $\frac{a+b} {2} = \frac{b-c} {2} + M$ where $a,b,c$ are any integer numbers and $M$ is any integer constant. Chef finds a triplet $(a,b,c)$ interesting if it satisfy the above equation. An array will be interesting if it contains at least one such triplet in any order. One thing you sh