数据结构与算法（C语言版）__归并排序

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归并排序是对两个已经排序的数组合并在一起。
下面使用迭代的方式实现归并排序

#define _SCL_SECURE_NO_WARNINGS#include<iostream>#include<algorithm>using namespace std;template<class T>void Merge(T *initList, T *mergedList, const int l, const int m, const int n){    int i1, i2, iResult;    for (i1 = l, i2 = m + 1, iResult = l; i1 <= m && i2 <= n; iResult++){        if (initList[i1] <= initList[i2]){            mergedList[iResult] = initList[i1];            i1++;        }        else{            mergedList[iResult] = initList[i2];            i2++;        }    }    copy(initList + i1, initList + m + 1, mergedList + iResult);    copy(initList + i2, initList + n + 1, mergedList + iResult);}int main(){    int a[] = { 0, 23, 47, 81, 95, 7, 14, 39, 55, 62, 74 };    int b[11] = { 0 };    Merge(a, b, 1, 4, 10);    for (int i = 1; i < 11; ++i){        cout << b[i] << " ";    }    cout << endl;    system("pause");    return 0;}

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下面看一步一步进行归并排序

#define _SCL_SECURE_NO_WARNINGS#include<iostream>#include<algorithm>using namespace std;template<class T>void Merge(T *initList, T *mergedList, const int l, const int m, const int n){    int i1, i2, iResult;    for (i1 = l, i2 = m + 1, iResult = l; i1 <= m && i2 <= n; iResult++){        if (initList[i1] <= initList[i2]){            mergedList[iResult] = initList[i1];            i1++;        }        else{            mergedList[iResult] = initList[i2];            i2++;        }    }    copy(initList + i1, initList + m + 1, mergedList + iResult);    copy(initList + i2, initList + n + 1, mergedList + 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);    }}int main(){    /*int a[] = { 0, 23, 47, 81, 95, 7, 14, 39, 55, 62, 74 };    int b[11] = { 0 };    Merge(a, b, 1, 4, 10);    for (int i = 1; i < 11; ++i){        cout << b[i] << " ";    }    cout << endl;*/    int m[] = { 0, 26, 5, 77, 1, 61, 11, 59, 15, 48, 19 };    int n[11] = { 0 };    MergePass(m, n, 10, 1);    for (int i = 1; i < 11; i++)        cout << n[i] << " ";    cout << endl;    MergePass(n, m, 10, 2);    for (int i = 1; i < 11; i++)        cout << m[i] << " ";    cout << endl;    MergePass(m, n, 10, 4);    for (int i = 1; i < 11; i++)        cout << n[i] << " ";    cout << endl;    MergePass(n, m, 10, 8);    for (int i = 1; i < 11; i++)        cout << m[i] << " ";    cout << endl;    system("pause");    return 0;}

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下面看整体的归并排序：

#define _SCL_SECURE_NO_WARNINGS#include<iostream>#include<algorithm>using namespace std;template<class T>void Merge(T *initList, T *mergedList, const int l, const int m, const int n){    int i1, i2, iResult;    for (i1 = l, i2 = m + 1, iResult = l; i1 <= m && i2 <= n; iResult++){        if (initList[i1] <= initList[i2]){            mergedList[iResult] = initList[i1];            i1++;        }        else{            mergedList[iResult] = initList[i2];            i2++;        }    }    copy(initList + i1, initList + m + 1, mergedList + iResult);    copy(initList + i2, initList + n + 1, mergedList + 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 *a, const int n){    T *tempList = new int[n + 1];    for (int l = 1; l < n; l *= 2){        MergePass(a, tempList, n, l);        l *= 2;        MergePass(tempList, a, n, l);    }    delete[]tempList;//删除临时的数组，防止内存泄露。}int main(){    /*int a[] = { 0, 23, 47, 81, 95, 7, 14, 39, 55, 62, 74 };    int b[11] = { 0 };    Merge(a, b, 1, 4, 10);    for (int i = 1; i < 11; ++i){        cout << b[i] << " ";    }    cout << endl;*/    int m[] = { 0, 26, 5, 77, 1, 61, 11, 59, 15, 48, 19 };    int n[11] = { 0 };    MergePass(m, n, 10, 1);    for (int i = 1; i < 11; i++)        cout << n[i] << " ";    cout << endl;    MergePass(n, m, 10, 2);    for (int i = 1; i < 11; i++)        cout << m[i] << " ";    cout << endl;    MergePass(m, n, 10, 4);    for (int i = 1; i < 11; i++)        cout << n[i] << " ";    cout << endl;    MergePass(n, m, 10, 8);    for (int i = 1; i < 11; i++)        cout << m[i] << " ";    cout << endl;    cout << "上面是中间数据测试" << endl;    cout << "下面是MergeSort...:" << endl;    int x[] = { 0, 26, 5, 77, 1, 61, 11, 59, 15, 48, 19 };    MergeSort(x, 10);    for (int i = 1; i < 11; i++)        cout << x[i] << " ";    cout << endl;    system("pause");    return 0;}

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总结：归并排序的速度和快速排序一样，使用三个函数写成一个归并排序，唯一的缺点是需要使用两倍的内存，如果要排序1M的数据，就要使用2M的内存，因为使用了临时数组。但是现在电脑内存都比较大，所以这个问题也不算严重。

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