find & count in C++

Three questions about a vector, each answered in one algorithm call instead of a hand-rolled loop.

#include <algorithm>
#include <vector>

bool found_enough(const std::vector<int>& v, int target) {
    auto hit = std::ranges::find(v, target);  // iterator, or end()
    auto zeros = std::ranges::count(v, 0);
    auto evens = std::ranges::count_if(v, [](int x) { return x % 2 == 0; });
    return hit != v.end() && zeros == 0 && evens >= 2;
}

How it works

1. std::ranges::find returns an iterator to the first match, or v.end() when there is none.
2. std::ranges::count tallies exact matches; here it checks that no element is 0.
3. std::ranges::count_if takes a lambda, counting the evens; the three answers combine into one bool.

Keywords and builtins used here

• auto
• bool
• const
• found_enough
• int
• return

The run, in numbers

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Step 3 of 3 in Algorithms, step 15 of 27 in Language basics.

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