Bi-increasing vector

In this problem, we say that a vector with $n$ integer numbers @v[0..@ $n-1$ @]@ is bi-increasing if $n \ge 2$ , @v[0]@ $>$ @v[@ $n-1$ @]@, and there exists an index $j$ between $0$ and $n-2$ such that:

@v[0]@ $\le \ldots \le$ @v[@ $j-1$ @]@ $\le$ @v[@ $j$ @]@,
@v[@ $j+1$ @]@ $\le$ @v[@ $j+2$ @]@ $\le \ldots \le$ @v[@ $n-1$ @]@.

For instance, the vector @[12, 12, 15, 20, 1, 3, 3, 5, 9]@ is bi-increasing (with $j = 3$ ).

Implement an efficient function

    bool search(int x, const vector<int>& v);

such that, given an integer number @x@ and a bi-increasing vector @v@, returns if @x@ is in @v@ or not. You can use and implement auxiliary functions if you need them.

Precondition

The vector @v@ is bi-increasing.

Observation

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

Problem information

Author: Unknown
Translator: Salvador Roura

Generation: 2026-01-25T12:22:49.921Z