std::ranges::is_heap

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本文介绍了如何使用C++标准库中的`<algorithm>`实现堆排序，并展示了如何将排序后的向量转换为对应的二叉树结构。通过`std::ranges::is_heap`检查堆性质，然后使用递归函数`draw_heap`展示堆的可视化形式。

https://en.cppreference.com/w/cpp/algorithm/ranges/is_heap

#include <algorithm>
#include <bit>
#include <cmath>
#include <iostream>
#include <vector>
 
void out(const auto& what, int n = 1) { while (n-- > 0) std::cout << what; }
 
void draw_heap(auto const& v);
 
int main()
{
    std::vector<int> v { 3, 1, 4, 1, 5, 9, 2, 6, 5, 3, 5, 8, 9, 7, 9, 3, 2, 3, 8 };
 
    out("initially, v:\n");
    for (auto i : v) std::cout << i << ' ';
    out('\n');
 
    if (!std::ranges::is_heap(v)) {
        out("making heap...\n");
        std::ranges::make_heap(v);
    }
 
    out("after make_heap, v:\n");
    for (auto t{1U}; auto i : v) {
        std::cout << i << (std::has_single_bit(++t) ? " │ " : " ");
    }
 
    out("\n" "corresponding binary tree is:\n");
    draw_heap(v);
}
 
void draw_heap(auto const& v)
{
    auto bails = [](int n, int w) {
        auto b = [](int w) { out("┌"), out("─", w), out("┴"), out("─", w), out("┐"); };
        n /= 2;
        if (!n) return;
        for (out(' ', w); n-- > 0; ) b(w), out(' ', w + w + 1);
        out('\n');
    };
    auto data = [](int n, int w, auto& first, auto last) {
        for(out(' ', w); n-- > 0 && first != last; ++first)
            out(*first), out(' ', w + w + 1);
        out('\n');
    };
    auto tier = [&](int t, int m, auto& first, auto last) {
        const int n {1 << t};
        const int w {(1 << (m - t - 1)) - 1};
        bails(n, w), data(n, w, first, last);
    };
    const int m {static_cast<int>(std::ceil(std::log2(1 + v.size())))};
    auto first {v.cbegin()};
    for (int i{}; i != m; ++i) { tier(i, m, first, v.cend()); }
}