链式二叉树（3）

#include<stdio.h>
#include<stdlib.h>
#include<string.h>
#include<assert.h>
#include<math.h>
//二叉树节点结构体
typedef int BTDataType;
typedef struct BinaryTreeNode
{
  BTDataType data;
  struct BinaryTreeNode* left;
  struct BinaryTreeNode* right;//
}BTNode;
//手动建造一个二叉树
//放入数据，左右置为NULL
BTNode* BuyNode(int x)
{
  BTNode* tmp = (BTNode*)malloc(sizeof(BTNode));
  assert(tmp);
  if (tmp == NULL)
  {
    perror("malloc fail");
    return;
  }
  tmp->data = x;
  tmp->left = NULL;
  tmp->right = NULL;
  return tmp;
}
//放入数据链接成树
BTNode* CreatBinaryTree()
{
  BTNode* node1 = BuyNode(1);
  BTNode* node2 = BuyNode(2);
  BTNode* node3 = BuyNode(3);
  BTNode* node4 = BuyNode(4);
  BTNode* node5 = BuyNode(5);
  BTNode* node6 = BuyNode(6);
  //BTNode* node7 = BuyNode(1);
  node1->left = node2;
  node1->right = node4;
  node2->left = node3;
  node4->left = node5;
  node4->right = node6;
  return node1;
}
//前序
void PreOrder(BTNode* root)
{
  if (root == NULL)
  {
    printf("N ");
    return;
  }
  printf("%d ", root->data);//根
  PreOrder(root->left);//左
  PreOrder(root->right);//右
}

int main()
{
  BTNode* root = CreatBinaryTree();
  int treeKsize=BinaryTreeLevelKSize(root, 3);
  printf("%d ", treeKsize);
  printf("\n");
  PreOrder(root);
  BTNode* FindX = BinaryTreeFind(root, 5);
  FindX->data = 7;
  printf("\n");
  PreOrder(root);
  return 0;
}

// 二叉树第k层节点个数
int BinaryTreeLevelKSize(BTNode* root, int k)
{
  if (root == NULL)
  {
    return 0;
  }
  if (k == 1)//到第k层就回归
  {
    return 1;
  }
  return BinaryTreeLevelKSize(root->left, k - 1) + BinaryTreeLevelKSize(root->right, k - 1);
}

// 二叉树查找值为x的节点
BTNode* BinaryTreeFind(BTNode* root, BTDataType x)
{
  if (root == NULL)
  {
    return NULL;
  }
  if (root->data == x)
  {
    return root;
  }
  BTNode* left = BinaryTreeFind(root->left, x);
  if (left)
  {
    return left;
  }
  BTNode* right = BinaryTreeFind(root->right, x);
  if (right)
  {
    return right;
  }
  return NULL;
}