归并排序非递归和递归实现

归并排序非递归实现:

#include <iostream>

using namespace std;

typedef int Type;

void Merge(Type c[], Type d[], int l, int m, int r)
{
// 合并c[l:m]和c[m+1:r]到d[1:r]
int i = l, j = m + 1, k = l;
while (i <= m && j <= r) {
if (c[i] <= c[j]) {
d[k++] = c[i++];
} else {
d[k++] = c[j++];
}
}
if (i > m) {
for (int q = j; q <= r; q++) {
d[k++] = c[q];
}
} else {
for (int q = i; q <= m; q++) {
d[k++] = c[q];
}
}
}

void MergePass(Type x[], Type y[], int s, int n)
{
// 合并大小为s的相邻子组
int i = 0;
while (i <= n - 2 * s) {
// 合并大小为s的相邻2段子数组
Merge(x, y, i, i + s - 1, i + 2 * s - 1);
i = i + 2 * s;
}
// 剩下的元素少于2s
if ( i + s < n ) {
Merge(x, y, i, i + s - 1, n - 1);
} else {
for (int j = i; j <= n - 1; j++) {
y[j] = x[j];
}
}
}

void MergeSort(Type a[], int n)
{
Type *b = new Type
;
int s = 1;
while (s < n) {
MergePass(a, b, s, n);      // 合并到数组b
s += s;
MergePass(b, a, s, n);      // 合并到数组a
s += s;
}
delete[] b;
}

void print(Type a[], int n)
{
for (int i=0; i<n; ++i) {
cout << a[i] << " ";
}
cout << endl;
}

int main(int argc, char *argv[])
{
Type a[6] = {1, 5, 2, 3, 6, 4};

MergeSort(a, 6);
print(a, 6);

return 0;
}

归并排序递归实现:

#include <iostream>

using namespace std;

typedef int Type;

Type *B = new Type[6];         // 和数组A一样大

void Merge(Type A[], int low, int mid, int high)
{
int i, j, k;

for (k = low; k <= high; ++k) {
B[k] = A[k];                    // 将A中所有元素复制到B
}

for (i = low, j = mid + 1, k = i; i <= mid && j <= high; ++k) {
if (B[i] <= B[j]) {
// 比较B的左右两段序列中的元素
A[k] = B[i++];              // 将较小值复制到A中
} else {
A[k] = B[j++];
}
}
while (i <= mid) {
A[k++] = B[i++];                // 若第一个表未检测完，复制
}
while (j <= high) {
A[k++] = B[j++];                // 若第二个表未检测完，复制
}
}

void MergeSort(Type A[], int low, int high)
{

if (low < high) {
int mid = (low + high) / 2;
MergeSort(A, low, mid);         // 对左侧子序列进行递归排序
MergeSort(A, mid+1, high);      // 对右侧子序列进行递归排序
Merge(A, low, mid, high);       // 归并
}
}

void print(Type A[], int n)
{
for (int i=0; i<n; ++i) {
cout << A[i] << " ";
}
cout << endl;
}

int main(int argc, char *argv[])
{
Type a[6] = {1, 5, 2, 3, 6, 4};

MergeSort(a, 0, 5);
print(a, 6);

delete[] B;

return 0;
}