《算法导论》第六章堆排序代码实现

int parent(const int &root) {
	return root / 2;
}

int left(const int &root) {
	return root * 2;
}

int right(const int &root) {
	return root * 2 + 1;
}

void max_heapify(vector<int> &nums, int i, const int &heap_size) {
	int largest;
	while (i <= heap_size) {
		largest = i;
		if (left(i) <= heap_size && nums[left(i)] > nums[i])
			largest = left(i);
		if (right(i) <= heap_size && nums[right(i)] > nums[largest])
			largest = right(i);
		if (largest == i)
			break;
		int temp = nums[largest];
		nums[largest] = nums[i];
		nums[i] = temp;
		i = largest;
	}
}

void build_max_heap(vector<int> &nums) {
	for (int i((nums.size() - 1) / 2); i >= 1; --i)
		max_heapify(nums, i, nums.size() - 1);
}

void heap_sort(vector<int> &nums) {
	nums.insert(nums.begin(), 0);//这里为了下标运算与书上一致，在数列头插了一个零，真正的待排序数列下标从1开始
	build_max_heap(nums);
	for (int i(nums.size() - 1); i > 1; --i) {
		int temp = nums[i];
		nums[i] = nums[1];
		nums[1] = temp;
		max_heapify(nums, 1, i - 1);
	}
	nums.erase(nums.begin());
}