MERGE_SORT归并排序C++实现

以下实现归并排序，第一部分含有哨兵（算法来自《算法导论》），第二部分不含哨兵

第一部分，含有哨兵的归并排序：

#include<iostream>

using namespace std;

void myMERGE(int * A, int p, int q, int r)

{

int n1 = q - p + 2;

int n2 = r - q + 1;

int L[n1];

int R[n2];

for(int i = 0; i < n1-1; ++i)

L[i] = A[p + i];

L[n1-1] = INT_MAX;

for(int j = 0; j < n2-1; ++j)

R[j] = A[q + j + 1];

R[n2-1] = INT_MAX;

int i = 0;

int j = 0;

for(int k = p; k <= r; ++k)

A[k] = L[i] < R[j] ? L[i++] : R[j++];

}

void MERGE_SORT(int *A, int p, int r)

{

if(r > p)

{

int q = (r + p) / 2;

MERGE_SORT(A, p, q);

MERGE_SORT(A, q+1, r);

myMERGE(A, p, q, r);

}

}

int main()

{

int b[4] = {4,3,2,1};

MERGE_SORT(b,0,3);

for(int i = 0; i < 4; ++i)

cout << b[i] << endl;

return 0;

}

-----------------------------------------------------

#include<iostream>

using namespace std;

void myMERGE(int *A, int p, int q, int r)

{

int n1 = q - p + 2;

int n2 = r - q + 1;

int L[n1];

int R[n2];

for(int i = 0; i < n1 - 1; ++ i)

{

L[i] = A[p + i];

}

L[n1 - 1] = 0;

for(int j = 0; j < n2 - 1; ++ j)

{

R[j] = A[q + 1 + j];

}

R[n2 - 1] = 0;

int i = 0;

int j = 0;

for(int k = p; k <= r; ++k)

{

A[k] = L[i] > R[j] ? L[i++] : R[j++];

}

}

void MERGE_DESCSORT(int *A, int p, int r)

{

if(r > p)

{

int q = (r + p) / 2;

MERGE_DESCSORT(A, p, q);

MERGE_DESCSORT(A, q + 1, r);

myMERGE(A, p, q, r);

}

}

int main()

{

int b[] = {1,2,3,4,5};

MERGE_DESCSORT(b, 0, 4);

for(int i = 0; i < 5; ++i)

{

cout << b[i] << endl;

}

return 0;

}

第二部分，不含有哨兵的归并排序：

#include<iostream>

using namespace std;

void myMERGE2(int *A, int p, int q, int r)

{

int n1 = q - p + 1;

int n2 = r - q;

int L[n1];

int R[n2];

for(int i = 0; i < n1; ++i)

L[i] = A[p + i];

for(int j = 0; j < n2; ++j)

R[j] = A[q + 1 + j];

int i = 0;

int j = 0;

int k = p;

while(i < n1 && j < n2)

A[k++] = L[i] < R[j]?L[i++]:R[j++];

while(i < n1)

A[k++] = L[i++];

while(j < n2)

A[k++] = R[j++];

}

void MERGE_SORT2(int *A, int p, int r)

{

if(p < r)

{

int q = (r + p) / 2;

MERGE_SORT2(A, p, q);

MERGE_SORT2(A, q + 1, r);

myMERGE2(A, p, q, r);

}

}

int main()

{

int b[] = {5,4,3,2,1};

MERGE_SORT2(b,0,4);

for(int i = 0; i < 5; ++i)

cout << b[i] << endl;

return 0;

}