一、歸併排序思想

基本思想：採用分治演算法，將要排序的陣列分為兩個部分，先分別對這兩個部分進行排序，然後再將兩部分已經排好序的子陣列進行合併，最後形成一個有序的陣列。

二、時間複雜度為

三、原始碼示例

#include "stdafx.h"
#define N 6

int A[N] = {9,4,1,6,8,7};

/*
    陣列A[low...mid]和A[mid+1...high]已排好序，將其合併為一個有序陣列
*/
void Merge(int low, int mid, int high)
{
    int h, iptr, j, k;
    int
 
 B[N];
    h = low;
    iptr = low;
    j = mid + 1;
    while (h <= mid && j <= high)
    {
        if (A[h] <= A[j])
        {
            B[iptr] = A[h];
            h++;
        }
        else
        {
            B[iptr] = A[j];
            j++;
        }
        iptr++;
    }
    if
 
 (h > mid)
    {
        for (k = j; k <= high; k++)
        {
            B[iptr] = A[k];
            iptr++;
        }
    }
    else
    {
        for (k = h; k <= mid; k++)
        {
            B[iptr] = A[k];
            iptr++;
        }
    }
    for (k = low; k <= high; k++)
        A[k] = B[k];
}

void MergeSort(int
 
 low, int high)
{
    if (low < high)
    {
        int mid = (low + high) / 2;
        MergeSort(low, mid);
        MergeSort(mid + 1, high);
        Merge(low, mid, high);
    }
}

int main()
{
    printf("歸併排序前：\n");
    for (int i = 0; i < N; i++)
        printf("%d\t", A[i]);

    MergeSort(0, N - 1);
    printf("\n\n********************************************************\n\n歸併排序後：\n");
    for (int i = 0; i < N; i++)
        printf ("%d\t", A[i]);
    printf("\n\n\n\n");
    return 0;
}

四、結果截圖