歸併排序

思路見排序思想

自己處理的時候開始和結束的邊界問題總是處理不好，還需要多看幾遍
代碼：

#include <iostream>

using namespace std;

void merge(int *data,int start,int end,int *result);
void merge_sort(int *data, int start, int end, int *result);

void merge_sort(int *data, int start, int end, int *result)
{
    if(1 == end - start)//如果區間中只有兩個元素，則對這兩個元素進行排序
    {
        if(data[start] > data[end])
        {
            int temp  = data[start];
            data[start] = data[end];
            data[end] = temp;
        }
        return;
    }
    else if(0 == end - start)//如果只有一個元素，則不用排序
        return;
    else
    {
        //繼續劃分子區間，分別對左右子區間進行排序
        merge_sort(data,start,(end-start+1)/2+start,result);
        merge_sort(data,(end-start+1)/2+start+1,end,result);
        //開始歸併已經排好序的start到end之間的數據
        merge(data,start,end,result);
        //把排序後的區間數據複製到原始數據中去
        for(int i = start;i <= end;++i)
            data[i] = result[i];
    }
}

void merge(int *data,int start,int end,int *result)
{
    int left_length = (end - start + 1) / 2 + 1;//左部分區間的數據元素的個數
    int left_index = start;
    int right_index = start + left_length;
    int result_index = start;
    while(left_index < start + left_length && right_index < end+1)
    {
        //對分別已經排好序的左區間和右區間進行合併
        if(data[left_index] <= data[right_index])
            result[result_index++] = data[left_index++];
        else
            result[result_index++] = data[right_index++];
    }
    while(left_index < start + left_length)
        result[result_index++] = data[left_index++];
    while(right_index < end+1)
        result[result_index++] = data[right_index++];
}

int main()
{
    int data[] = {9,6,7,22,20,33,16,20};
    const int length = 8;
    int result[length];
    cout << "Before sorted:" << endl;
    for(int i = 0;i < length;++i)
        cout << data[i] << "  ";
    cout << endl;
    cout << "After sorted:" << endl;
    merge_sort(data,0,length-1,result);
    for(int i = 0;i < length;++i)
        cout << data[i] << "  ";
    cout << endl;
    system("pause");
    return 0;
}