Write an efficient function

that tells if *x* belongs to the vector *v* or not.

**Precondition**

The vector *v* is “almost sorted” in nondecreasing order,
in the sense that there may be at most a pair of indices *i* and *j*
such that 0 ≤ *i* < *j* < *n* and *V*[*i*] > *V*[*j*].

**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++