插入排序，快速排序，堆排序，归并排序

插入排序

void insert_sort(int arry[], int length)
{
  if(length < 2)
    return;

  for(int i = 1; i != length; ++i)
    if(arry[i-1] > arry[i]){
      int temp = arry[i], j;
      for(j = i-1; j >= 0 && arry[j] > temp; --j)
	arry[j+1] = arry[j];
      arry[j+1] = temp;
    }
}

快速排序

int quick_adj(int arry[], int low, int high)
{
  //将第一个，最后一个和中间一个元素中居中的元素选为枢轴
  if((arry[low] >= arry[(high+low)/2] && arry[low] <= arry[high]) || 
     (arry[low] >= arry[high] && arry[low] <= arry[(high+low)/2])){
    int temp = arry[low];
    arry[low] = arry[high];
    arry[high] = temp;
  }else if((arry[(high+low)/2] >= arry[low] && arry[(high+low)/2] <= arry[high]) || 
	   (arry[(high+low)/2] >= arry[high] && arry[(high+low)/2] <= arry[low])){
    int temp = arry[(high+low)/2];
    arry[(high+low)/2] = arry[high];
    arry[high] = temp;
  }
  int pivot = arry[high];
  
  while(low < high){
    while(arry[low] <= pivot && low < high)
      ++low;
    arry[high] = arry[low];
    while(arry[high] >= pivot && low < high)
      --high;
    arry[low] = arry[high];
  }
  arry[low] = pivot;
  return low;
}

void quick_sort(int arry[], int low, int high)
{
  if(low < high){
    int pivot = quick_adj(arry, low, high);
    quick_sort(arry, low, pivot-1);
    quick_sort(arry, pivot+1, high);
  }
}

堆排序

void heap_adj(int arry[], int low, int high)
{
  //大顶堆
  int temp = arry[low];
  for(int i = 2*low+1; i <= high; i = 2*i+1){
    if(i < high && arry[i] < arry[i+1])
      ++i;
    if(arry[i] <= temp)
      break;
    arry[low] = arry[i];
    low = i;
  }
  arry[low] = temp;
}

void heap_sort(int arry[], int length)
{
  for(int i = (length-1)/2; i >= 0; --i)
    heap_adj(arry, i, length-1);
  for(int i = length-1; i > 0; --i){
    int temp = arry[0];
    arry[0] = arry[i];
    arry[i] = temp;
    heap_adj(arry, 0, i-1);
  }
}

归并排序

void merge(int arry[], int* temp, int low, int mid, int high)
{
  int i, j, k;
  for(i = low, j = mid+1, k = low; i <= mid && j <= high; ++k){
    if(arry[i] < arry[j])
      temp[k] = arry[i++];
    else
      temp[k] = arry[j++];
  }  
  while(i <= mid)
    temp[k++] = arry[i++];
  while(j <= high)
    temp[k++] = arry[j++];
  while(--k >= low)
    arry[k] = temp[k];
}

void m_sort(int arry[], int* temp, int low, int high)
{
  if(low < high){
    int mid = (low+high)/2;
    m_sort(arry, temp, low, mid);
    m_sort(arry, temp, mid+1, high);
    merge(arry, temp, low, mid, high);
  }
}

void merge_sort(int arry[], int low, int high)
{
  int* p = new int[high-low+1];
  m_sort(arry, p, low, high);
  delete[] p;
}

使用c标准库提供的rand()函数随机产生20万个[0,100]的整数，大致的排序时间为：插入排序43.47秒；快速排序0.67秒；堆排序0.05秒；归并排序0.05秒．另外直接调用C++algorithm的sort排序，耗时大致为0.04秒，标准库就是牛啊！