Search in a unimodal vector

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

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

For instance, the vector @[0, 2, 5, 7, 6, 5, 4, 3, 1]@ is unimodal (with $j = 3$ ).

Note that vectors with $n \leq 2$ different elements are unimodal. In general, note that any strictly increasing vector is also unimodal (and in all cases $j = n-1$ ), and analogously, any strictly decreasing vector is also unimodal (and then $j = 0$ ).

Implement an efficient function

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

such that, given an integer number @x@ and a unimodal vector @v@, returns true if @x@ appears in @v@, and false otherwise. You can use and implement auxiliary functions if you need them.

Precondition

The vector @v@ is unimodal.

Observation

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

Problem information

Author: Unknown
Translator: Prof. EDA

Generation: 2026-01-25T22:41:26.180Z