算法导论：快速排序和插入排序

代码实现

#ifndef _SORT_H
#define _SORT_H

// goal: quicksort and insertsort
// time: 12/2/2014
// author: zrss
// reference: introduction to algorithms

class Sort {
public:
    void quickSort(int A[], int p, int r);
    void insertSort(int A[], int p, int r);

private:
    int partition(int A[], int p, int r); // for quickSort
};

int Sort::partition(int A[], int p, int r) {
    int x = A[r]; // use A[r] as pivot node
    
    int i = p - 1; // point to left part

    // divide A array to three part
    // A[p - i] <= x
    // A[(i + 1) - j] > x
    // A[(j + 1) - r) unknown
    for (int j = p; j < r; ++j) {
        if (A[j] <= x) {
            ++i;
            if (i != j) { // swap A[i] and A[j]
                int temp = A[i];
                A[i] = A[j];
                A[j] = temp;
            }
        }
    }

    // exchange A[i + 1] and A[r]
    A[r] = A[i + 1];
    A[i + 1] = x;

    return (i + 1);
}

void Sort::quickSort(int A[], int p, int r) {
    if (p < r) {
        int q = partition(A, p, r);
        quickSort(A, p, q - 1);
        quickSort(A, q + 1, r);
    }
}

void Sort::insertSort(int A[], int p, int r) {
    for (int j = p + 1; j <= r; ++j) {
        int key = A[j];
        int i = j - 1;
        while (i >= p && A[i] > key) { // move backward
            A[i + 1] = A[i];
            --i;
        }

        if (i + 1 != j) { // insert A[j] to right position
            A[i + 1] = key;
        }
    }
}


#endif

插入排序与快速排序运行时间比较

随机产生100,000个int测试数据

#include <cstdio>
#include <cstdlib>
#include "windows.h"
#include "sort.h"

int main(void) {
    const int length = 100000;
    int number[length];

    for (int i = 0; i < length; ++i) {
        number[i] = rand();
    }

    Sort sort;

    DWORD st = GetTickCount();

    sort.insertSort(number, 0, length - 1);
    //sort.quickSort(number, 0, length - 1);

    DWORD ed = GetTickCount();

    printf("InsertSort use time: %dms
", ed - st);
    //printf("QuickSort use time: %dms
", ed - st);

    system("pause");
    return 0;
}

InsertSort use time: 2200ms

QuickSort use time: 0ms

系统信息

System: Windows 7 professional Service Pack 1

CPU: Intel(R) Pentium(R) Dual CPU E2220 @ 2.40GHz 2.40GHz

Memory: 3.00 GB

结论

在输入为100, 000数量级上，且输入的数据为随机值时，快速排序的效率优于插入排序