Number of unique solution

Question

Suppose there is an equation

$x_{1}+x_{2}+...........x_{r}=n$

Then number of unique solution in this given equation?

Comments

(n+r-1)! / (n!.(r-1)!) ???

---

@akash ,no. of non-negative solutions and no. of unique  solutions both are the same things ?

---

@ankit
no they are not same
that is why I asked the question

---

ok thanks !