Data Structures

In-Place Stable Partition

Difficulty

Asked at Jane Street, Two Sigma

Theory: Data Structures You Implement, Not Import

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xxxxxxxxxxxx xx xxxx. xxxxxxxxxxxx xxxxxx, xx xxxxx, xxxx xx xxxxxxx xxxxxx, xx x xxxxxxxxx xxxxxxxxx xxxxxxx, xxx xxx xxxxxxxx xxxx xxxxxx xx xx xxxxx xxxxxxx xxxxxxx xx xx xxx xxxx xxx xxxxxx xx-xxxxx xxxxx xxx xxxxxx xxx::xxxxxx_xxxxxxxxx xxxxxx.

xxxxxxxxx xxxxxx_xxxxxxxxx_xxxxxxx(xxxxxx, xxxx): xxxx xxxxxxxxxx xxxxxxxxxx xxxx xx xxx xxxxx, xxxx xxx xxxxxxxx xxxxx xx xxxx xxxxxx, xxx xxxxxx xxx xxxxx xx xxx xxxxx xxxxxxx xxxx xxxx xxx xxxxxxx xx.

{x, x, x, x, x, x} xxxx "xx xxxx"  ->  {x, x, x, x, x, x}, xxxxxxx x

xxx xxxxxx xxxxxxxx xxx xx xxxxxxxxxxxx, xx "xx xxxxx" xx xxxxxxxx xxxxxx xxxx xxxxxxx. xxx::xxxxxx xx xxxxxxxxx xxx xxxxxxxxx xxxxxxx.

xxxxxxxx

xxx::xxxxxx<xxxx xxxx> x{xx, x, xx, x, xx, x, xx, x};
xxxxxx_xxxxxxxxx_xxxxxxx(x, [](xxxx xxxx x) { xxxxxx x >= xx; });
// x xx {xx, xx, xx, xx, x, x, x, x}, xxxxxxx x

xxxx xxxxxx xxxx xxx xx xxx xxxxx xxxx xxxx xx. xxxx xx xxx xxxxxxxxxxx, xxx xx xx xxxx xxxxx xxx xxx xxxxxxx xxxxxxxxx.

xxxxxxxxxxx

xx xx ( x xxxxx xx^x ) xxxxxxxx, xxx xxxx xxxxxxxxxxx.
xxx xxx-xxxxxxx xxxx xxxxxxxxx xxxxxx xxx xx xxxxxxxx xxxxxxxxx xx ( x(x) ) xxx xxxxxxxxx xxxx xxxxxx. xxxxxxx xx xxx xxxxxxxxx xx xxxxxx xxxx xx xxx xxxx xx, xxx xxxx xxx x xxxxxxxxxx xxxx xx xx x xxxxxxxxx.
xxxxxxx xxx xxxxxxx xxxx xxx xxxxxx xxx xxx xxxx xxxx xxxxxxx xx xxx xxxxxxx xxxxxx xxxxxx xxx xxxxx ( x(x) ) xxxxxxx, xxxxx xx xxxxxxx xxxx xx xxxxxxxxx xxxx.
( x(x xxx x) ) xxxxxxx xxxxx xx xxx xxxxxxxx xxxx. xxxx xx xxx xxxxx xx ( x(x) ) xxxxx, xxx xx xx xxx xxxx xxxxx xxx xxxxxxxx xxxxxxx xxxxx: xxx::xxxxxx_xxxxxxxxx xx xxxxxxxxxx xx ( x(x) ) xxxxx xx xx xxx xxxxxxxx xxx ( x(x xxx x) ) xx xx xxxxxx.

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Language: C++stable_partition_inplace

#include <algorithm>
#include <cstddef>
#include <cstdlib>
#include <new>
#include <vector>

// ...
// ...
// ...
// ...
namespace probe {
inline long long& counter() {
    static long long calls = 0;
    return calls;
}
inline long long allocations() { return counter(); }
inline void reset() { counter() = 0; }
}  // ...

void* operator new(std::size_t bytes) {
    ++probe::counter();
    void* p = std::malloc(bytes ? bytes : 1);
    if (!p) throw std::bad_alloc();
    return p;
}
void* operator new[](std::size_t bytes) { return ::operator new(bytes); }
void operator delete(void* p) noexcept { std::free(p); }
void operator delete[](void* p) noexcept { std::free(p); }
void operator delete(void* p, std::size_t) noexcept { std::free(p); }
void operator delete[](void* p, std::size_t) noexcept { std::free(p); }

// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
// ...
template <typename Pred>
std::size_t stable_partition_inplace(std::vector<long long>& values, Pred pred) {
    // ...
    (void)pred;
    return values.size();
}

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