线性建堆法

#include <iostream>
using namespace std;

void downUpdate(int *arr, int n, int ind) {
  while ((ind << 1) <= n) {
    int temp = ind, l = temp << 1, r = temp << 1 | 1;
    if (arr[temp] > arr[l]) temp = l;
    if (r <= n && arr[temp] > arr[r]) temp = r;
    if (temp == ind) break;
    swap(arr[temp], arr[ind]);
    ind = temp;
  }
  return;
}
void heap_sort(int* arr, int n) {
  arr -= 1;
  //建堆
  for (int i = n >> 1; i >= 1; i--) {
    downUpdate(arr, n, i);
  }
  //堆排序
  for (int i = n; i > 1; i--) {
    swap(arr[i], arr[1]);
    downUpdate(arr, i- 1, 1);
  }
  return;
}

void output(int* arr, int n) {
  printf("[");
  for (int i = 0; i < n; i++) {
    i&& printf(" ");
    printf("%d", arr[i]);
  }
  printf("]\n");
  return;
}
int main() {
  srand(time(0));
#define MAX_N 20
  int arr[MAX_N] = { 0 };
  for (int i = 0; i < MAX_N; i++) {
    arr[i] = rand() % 100;
  }
  output(arr, MAX_N);
  heap_sort(arr, MAX_N);
  output(arr, MAX_N);
#undef MAX_N
  return 0;
}