二叉树基础知识

#include<stdio.h>
struct TreeNode{
    int val;
    TreeNode *left;
    TreeNode *right;
    TreeNode(int x) : val(x),left(NULL),right(NULL){}
};
void preorder_print(TreeNode *node, int layer){
    if(!node){
        return;
    }
    for(int i = 0; i < layer; i++){
    }
    printf("{%d}\n",node->val);
    preorder_print(node->left, layer + 1);//遍历左子树，层数+1
    preorder_print(node->right, layer + 1);//遍历右子树，层数+1
}
int main(){
    TreeNode a(1);
    TreeNode b(2);
    TreeNode c(5);
    TreeNode d(3);
    TreeNode e(4);
    TreeNode f(6);
    a.left = &b;
    a.right = &c;
    b.left = &d;
    b.right = &e;
    c.right = &f;
    preorder_print = (&a,0);
    return 0;
}

void traversal_qian(TreeNode * node, int layer){
    if(!node){
        return;
    }
for(int i = 0;i < layer;i++){
    printf("-----");
}
printf("[%d\n]",node->val);
traversal_qian(node->left, layer +1);
traversal_qian(node->right,layer+1);
}