分治算法与合并排序示例

#include <stdio.h>
#include <memory.h>
#include <algorithm>

using namespace std;

#define MAX_N 10

void merge_sort(int seq[], int len);

// 打印数组
void my_print(int seq[], int len)
{
    for (int i = 0; i < len; i++)
        printf("%d\n", seq[i]);
}

int main()
{
    int arr[] = {9, 8, 7, 6, 1, 3, 2, 4, 5, 0};
    merge_sort(arr, MAX_N);

    my_print(arr, MAX_N);
    return 0;
}

// 归并
void merge(int seq[], int s1[], int l1, int s2[], int l2)
{
    int i = 0, j = 0, k = 0;

    while(i < l1 && j < l2) {
        if (s1[i] < s2[j])
            seq[k++] = s1[i++];
        else
            seq[k++] = s2[j++];
    }

    while (i < l1)
        seq[k++] = s1[i++];

    while (j < l2)
        seq[k++] = s2[j++];
}

// 分治递归
void merge_sort_rec(int seq[], int len)
{
    if (len < 4) {
        sort(seq, seq+len); // 不复杂化了，主要体现以下分治算法和合并排序
    }
    else {
        int l1 = len / 2, l2 = len - l1;

        int *pSeq1 = new int[l1];
        int *pSeq2 = new int[l2];
        memcpy(pSeq1, seq, sizeof(int)*l1);
        memcpy(pSeq2, seq+l1, sizeof(int)*l2);

        merge_sort_rec(pSeq1, l1); // 分治
        merge_sort_rec(pSeq2, l2); // 分治

        merge(seq, pSeq1, l1, pSeq2, l2); // 合并

        delete[] pSeq1;
        delete[] pSeq2;
    }
}

//合并排序对外接口
void merge_sort(int seq[], int len)
{
    merge_sort_rec(seq, len);
}