For the conversion, we need a so-called**hash function**.

The goal of it is to convert a string into an integer, the so-called**hash** of the string.

The following condition has to hold: if two strings $s$ and $t$ are equal ($s = t$), thenalsotheir hashes have to be equal ($\text{hash}(s) = \text{hash}(t)$).

The following condition has to hold: if two strings $s$ and $t$ are equal ($s = t$), then their hashes also have to be equal ($\text{hash}(s) = \text{hash}(t)$).

Otherwise, we will not be able to compare strings.

Notice, the opposite direction doesn't have to hold.