Decryption

Alice wants to share a message $M$ with Bob. $M$ is an array of integers of length $N$ and $M[i] \geq 1$ for every $1 \leq i \leq N$. But instead of sending $M$ directly, he first encrypts it and then sends the encrypted message. Let's denote the encryption of $M$ by $F$. For encrypting the message $M$ Alice chooses one subarray of $M$ having at least $X$ distinct integers and changes each elem