排序算法之归并排序

1、迭代归并排序

将两个数当做已经排好序，再进行归并排序；然后再将上面两个排好序的数据进行归并排序；依次类推，最后将所有数据归并排序。如下图所示：
这里写图片描述

2、归并排序demo

#include <iostream>

using namespace std;

template <class T>
void merge(T *initList, T *mergeList, int f, int s, int l);

template <class T>
void mergePass(T *initList, T *mergeList, const int n, const int s);

template <class T>
void mergeSort(T *initList, const int n);

int main(int argc, const char *argv[])
{
    /*
    cout << "初始数据：" << endl;
    int a[] = {0, 1, 14, 45, 56, 16, 27, 46, 57, 78, 88};
    int b[11] = {0};
    for (int i = 1; i < 11; i++){
        cout << a[i] << " ";
    }
    cout << endl;

    cout << "开始测试merge..." << endl;
    merge(a, b, 1, 4, 10);
    for (int i = 1; i < 11; i++){
        cout << b[i] << " ";
    }

    cout << endl;
    cout << endl;

    cout << "初始数据：" << endl;
    int x[] = {0, 26, 5, 77, 1, 61, 11, 59, 15, 48, 19};
    int y[11];
    for (int i = 1; i < 11; i++){
        cout << x[i] << " ";
    }
    cout << endl;

    cout << "开始测试mergePass..." << endl;
    mergePass(x, y, 10, 1);
    for (int i = 1; i < 11; i++){
        cout << y[i] << " ";
    }
    cout << endl;

    mergePass(y, x, 10, 2);
    for (int i = 1; i < 11; i++){
        cout << x[i] << " ";
    }
    cout << endl;

    mergePass(x, y, 10, 4);
    for (int i = 1; i < 11; i++){
        cout << y[i] << " ";
    }
    cout << endl;

    mergePass(y, x, 10, 8);
    for (int i = 1; i < 11; i++){
        cout << x[i] << " ";
    }

    cout << endl;
    cout << endl;
*/
    cout << "初始数据：" << endl;
    int data[] = {0, 26, 5, 77, 1, 61, 11, 59, 15, 48, 19}; //注意：data[0],只是为了变成方便，不作为排序数据
    for (int i = 1; i < 11; i++){
        cout << data[i] << " ";
    }
    cout << endl;

    cout << "开始测试mergeSort..." << endl;
    mergeSort(data, 10);
    for (int i = 1; i < 11; i++){
        cout << data[i] << " ";
    }
    cout << endl;

    return 0;
}

template <class T>
void merge(T *initList, T *mergeList, int f, int s, int l)
{
    int i, j, iResult;
    for (i = f, j = s + 1, iResult = f; i <= s && j <= l; iResult++){
        if (initList[i] < initList[j]){
            mergeList[iResult] = initList[i];
            i++;
        }
        else {
            mergeList[iResult] = initList[j];
            j++;
        }
    }

    copy(initList+i, initList+s+1, mergeList+iResult);
    copy(initList+j, initList+l+1, mergeList+iResult);
}

template <class T>
void mergePass(T *initList, T *resultList, const int n, const int s)
{
    int i;
    for (i = 1; i <= n-2*s+1; i += 2*s)
        merge(initList, resultList, i, i+s-1, i+2*s-1);

    if ((i+s-1) < n)
        merge(initList, resultList, i, i+s-1, n);
    else
        copy(initList+i, initList+n+1, resultList+i);
}

template <class T>
void mergeSort(T *initList, const int n)
{
    T *tempList = new int[n+1];
    for (int i = 1; i < n; i *= 2){
        mergePass(initList, tempList, n, i);
        i *= 2;
        mergePass(tempList, initList, n, i);
    }

    delete[] tempList;
}