面试必考三大排序算法C++代码（快速排序、归并排序、堆排序）

前两个为C++风格代码，后一个为C风格代码，除了输入输出，其它无差别，但C输入输出要比C++更快。

快速排序

#include <iostream>
using namespace std;

void swap(int num[], int i, int j)
{
    int temp = num[i];
    num[i] = num[j];
    num[j] = temp;
}

int partition(int num[], int left, int right)
{
    int key = left;
    int value = num[key];
    while (left < right)
    {
        while (left < right && num[right] >= value)right--;
        while (left < right && num[left] <= value)left++;
        swap(num, right, left);
    }
    swap(num, key, left);
    return left;
}

void QuickSort(int num[], int begin, int end)
{
    if (begin < end)
    {
        int middle = partition(num, begin, end);
        QuickSort(num, begin, middle - 1);
        QuickSort(num, middle + 1, end);
    }
}

int main()
{
    int num[100];
    int n = 0;
    while (cin >> n)
    {
        for (int i = 0; i < n; i++)
        {
            int temp = 0;
            cin >> temp;
            num[i] = temp;
        }
        QuickSort(num, 0, n - 1);
        for (int i = 0; i < n; i++)
            cout << num[i] << " ";
        cout << endl;
    }
    return 0;
}

归并排序

#include <iostream>
using namespace std;

void Merge(int *from, int *to, int begin, int middle, int end)
{
    int i = begin;
    int j = middle + 1;
    int k = i;
    while (i <= middle && j <= end)
    {
        if (from[i] < from[j])
            to[k++] = from[i++];
        else to[k++] = from[j++];
    }
    while (i <= middle) to[k++] = from[i++];
    while (j <= end) to[k++] = from[j++];
}

void MergePass(int *from, int *to, int end, int h)
{
    int i = 0;
    while (i <= end - 2 * h + 1)
    {
        Merge(from, to, i, i + h - 1, i + 2 * h - 1);
        i += 2 * h;
    }
    if (i < end - h + 1)
        Merge(from, to, i, i + h - 1, end);
    else
        for (int k = i; k <= end; k++)
        {
            to[k] = from[k];
        }
}

void MergeSort(int *from, int *to, int begin, int end)
{
    int h = 1;
    while (h <= end)
    {
        MergePass(from, to, end, h);
        h = 2 * h;
        MergePass(to, from, end, h);
        h = 2 * h;
    }
}

int main() {
    int num[100];
    int num2[100];
    int n = 0;
    while (cin >> n)
    {
        for (int i = 0; i < n; i++)
        {
            int temp = 0;
            cin >> temp;
            num[i] = temp;
        }
        MergeSort(num, num2, 0, n - 1);
        for (int i = 0; i < n; i++)
            cout << num[i] << " ";
        cout << endl;
    }
    return 0;
}

堆排序

#include <stdio.h>

void HeapAdjust(int *num, int s, int length)
{
    int temp = num[s];
    int child = 2 * s + 1;
    while (child < length)
    {
        if (child + 1 < length && num[child] < num[child + 1])
            child++;
        if (num[s] < num[child])
        {
            num[s] = num[child];
            num[child] = temp;
            s = child;
            child = 2 * s + 1;
        }
        else
            break;
    }
}

void buildingHeap(int *num, int length)
{
    for (int i = (length - 1) / 2; i >= 0; --i)
        HeapAdjust(num, i, length);
}

void HeapSort(int *num, int length)
{
    buildingHeap(num, length);
    for (int i = length - 1; i > 0; --i)
    {
        int temp = num[0];
        num[0] = num[i];
        num[i] = temp;
        HeapAdjust(num, 0, i);
    }
}

void print(int num[], int n) {
    for (int i = 0; i < n; i++) {
        printf("%d ", num[i]);
    }
    printf("
");
}

int main()
{
    int num[100];
    int n = 0;
    while (scanf("%d", &n) != EOF)
    {
        for (int i = 0; i < n; i++)
            scanf("%d", &num[i]);
        HeapSort(num, n);
        print(num, n);
    }
    return 0;
}

验证OJ：https://www.nowcoder.com/practice/508f66c6c93d4191ab25151066cb50ef?tpId=69&&tqId=29657&rp=1&ru=/activity/oj&qru=/ta/hust-kaoyan/question-ranking