We know that among all numbers of factorial, only numbers with factor 2 and 5 can produce a trailing zero (`2*5 = 10`

), and that we will have much more factor 2's than factor 5's. So the key is to find the number of factor 5's we have in the factorial sequence, which is equivalent to the number of trailing zeros (the final solution to this problem).

I used an example to deduce the solution:

Suppose n = 100, then how many numbers with factors 5 do we have?

--> We have `1*5, 2*5, 3*5, ..., 20*5`

, a total of `100/5 = 20`

numbers.

Among the numbers `1-20`

, there also exists factor 5.

--> We have `1*5, 2*5, ..., 4*5`

a total of `20/5 = 4`

numbers.

And so on.

Thus, given a number `n`

, we can just repeat the following process:

```
Repeat while n > 0
1. Divide n by 5 to find numbers with factor 5 (add to result)
2. Set n = n / 5 to find remaining factor 5's
```

```
public class Solution {
public int trailingZeroes(int n) {
int result = 0;
while (n > 0) {
result += (n / 5);
n /= 5;
}
return result;
}
}
```