Write an efficient function

that returns the position of the first occurrence of *x* in the vector *v*.
If *x* does not belong to *v*, return a -1.

**Precondition**

The vector *v* is sorted in nondecreasing order.

**Observation**
You only need to submit the required procedure;
your main program will be ignored.

Information

- Author
- Salvador Roura
- Language
- English
- Official solutions
- C++
- User solutions
- C++