【愚公系列】2021年11月 C#版 数据结构与算法解析(选择排序-堆排序)

/// 
/// 堆排序
/// 
public class Program {

    public static void Main(string[] args) {
        int[] array = { 43, 69, 11, 72, 28, 21, 56, 80, 48, 94, 32, 8 };

        HeapSort(array);
        ShowSord(array);

        Console.ReadKey();
    }

    private static void ShowSord(int[] array) {
        foreach (var num in array) {
            Console.Write($"{num} ");
        }
        Console.WriteLine();
    }

    private static void HeapSort(int[] array) {
        MaxHeap(array);
        for (int i = array.Length - 1; i > 0; i--) {
            Swap(ref array[0], ref array[i]);
            Heapify(array, 0, i);
        }
    }

    private static void MaxHeap(int[] array) {
        for (int i = array.Length / 2 - 1; i >= 0; i--) {
            Heapify(array, i, array.Length);
        }
    }

    private static void Heapify(int[] array, int index, int size) {
        int left = 2 * index + 1;
        int right = 2 * index + 2;
        int large = index;

        if (left < size && array[left] > array[large]) {
            large = left;
        }
        if (right < size && array[right] > array[large]) {
            large = right;
        }
        if (index != large) {
            Swap(ref array[index], ref array[large]);
            Heapify(array, large, size);
        }
    }

    private static void Swap(ref int first, ref int second) {
        int t = first;
        first = second;
        second = t;
    }

}