归并排序 merge sort

https://github.com/hotwater99/practice_datastructure_and_algorithm.git

《数据结构与算法分析——C语言描述》机械工业出版社，原书第2版，7.6

归并排序是将待排序的数组分为两个子数组，分别排好序，然后再合并到一起。

使用到了分治的策略。

归并排序：

void Merge(int array[], int tmpArray[], int leftPos, int rightPos, int rightEnd)
{
  int i, leftEnd, total, tmp_pos;

  leftEnd = rightPos - 1;
  total = rightEnd - leftPos + 1;
  tmp_pos = leftPos;

  while (leftPos <= leftEnd && rightPos <= rightEnd) {
    if (array[leftPos] < array[rightPos]) {
      tmpArray[tmp_pos++] = array[leftPos++];
    }
    else {
      tmpArray[tmp_pos++] = array[rightPos++];
    }
  }

  while (leftPos <= leftEnd) {
    tmpArray[tmp_pos++] = array[leftPos++];
  }
  while (rightPos <= rightEnd) {
    tmpArray[tmp_pos++] = array[rightPos++];
  }

  for (i = 0; i < total; i++, rightEnd--) {
    array[rightEnd] = tmpArray[rightEnd];
  }
}

void MSort(int array[], int tmpArray[], int left, int right)
{
  int center;

  if (left < right) {
    center = (left + right) / 2;
    MSort(array, tmpArray, left, center);
    MSort(array, tmpArray, center + 1, right);
    Merge(array, tmpArray, left, center + 1, right);
  }
}

void MergeSort(int array[], int N)
{
  int *tmp_array;

  tmp_array = (int *)malloc(N * sizeof(int));
  if (tmp_array != NULL) {
    MSort(array, tmp_array, 0, N - 1);
    free(tmp_array);
  }
  else {
    // error
  }
}

完整代码：

#include <iostream>
#include <ctime>

using namespace std;

#define random(x)       (rand()%x)
#define ARRAY_LENTH     10

void Merge(int array[], int tmpArray[], int leftPos, int rightPos, int rightEnd)
{
  int i, leftEnd, total, tmp_pos;

  leftEnd = rightPos - 1;
  total = rightEnd - leftPos + 1;
  tmp_pos = leftPos;

  while (leftPos <= leftEnd && rightPos <= rightEnd) {
    if (array[leftPos] < array[rightPos]) {
      tmpArray[tmp_pos++] = array[leftPos++];
    }
    else {
      tmpArray[tmp_pos++] = array[rightPos++];
    }
  }

  while (leftPos <= leftEnd) {
    tmpArray[tmp_pos++] = array[leftPos++];
  }
  while (rightPos <= rightEnd) {
    tmpArray[tmp_pos++] = array[rightPos++];
  }

  for (i = 0; i < total; i++, rightEnd--) {
    array[rightEnd] = tmpArray[rightEnd];
  }
}

void MSort(int array[], int tmpArray[], int left, int right)
{
  int center;

  if (left < right) {
    center = (left + right) / 2;
    MSort(array, tmpArray, left, center);
    MSort(array, tmpArray, center + 1, right);
    Merge(array, tmpArray, left, center + 1, right);
  }
}

void MergeSort(int array[], int N)
{
  int *tmp_array;

  tmp_array = (int *)malloc(N * sizeof(int));
  if (tmp_array != NULL) {
    MSort(array, tmp_array, 0, N - 1);
    free(tmp_array);
  }
  else {
    // error
  }
}

int main() {
  int test_array[ARRAY_LENTH];
  int i, N = ARRAY_LENTH;
  clock_t start_time, stop_time;

  for (i = 0; i < N; i++) {
    test_array[i] = random(N);
  }

  if (N <= 100) {
    cout << "raw : ";
    for (i = 0; i < N; i++) {
      cout << test_array[i] << " ";
    }
    cout << endl;
  }

  start_time = clock();

  MergeSort(test_array, N);

  stop_time = clock();

  if (N <= 100) {
    cout << "sort: ";
    for (i = 0; i < N; i++) {
      cout << test_array[i] << " ";
    }
    cout << endl;
  }

  cout << "MergeSort(" << N << ")..." << endl;
  cout << "total time used: ";
  cout << (double)(stop_time - start_time) / CLOCKS_PER_SEC << "s" << endl;

  system("pause");

  return 0;
}

测试结果

---

N=10

raw : 1 7 4 0 9 4 8 8 2 4
sort: 0 1 2 4 4 4 7 8 8 9
MergeSort(10)...
total time used: 0s

N=100

raw : 41 67 34 0 69 24 78 58 62 64 5 45 81 27 61 91 95 42 27 36 91 4 2 53 92 82 21 16 18 95 47 26 71 38 69 12 67 99 35 94 3 11 22 33 73 64 41 11 53 68 47 44 62 57 37 59 23 41 29 78 16 35 90 42 88 6 40 42 64 48 46 5 90 29 70 50 6 1 93 48 29 23 84 54 56 40 66 76 31 8 44 39 26 23 37 38 18 82 29 41
sort: 0 1 2 3 4 5 5 6 6 8 11 11 12 16 16 18 18 21 22 23 23 23 24 26 26 27 27 29 29 29 29 31 33 34 35 35 36 37 37 38 38 39 40 40 41 41 41 41 42 42 42 44 44 45 46 47 47 48 48 50 53 53 54 56 57 58 59 61 62 62 64 64 64 66 67 67 68 69 69 70 71 73 76 78 78 81 82 82 84 88 90 90 91 91 92 93 94 95 95 99
MergeSort(100)...
total time used: 0s

N=1000

MergeSort(1000)...
total time used: 0s

N=10000

MergeSort(10000)...
total time used: 0.001s

N=100000

MergeSort(100000)...
total time used: 0.015s