Binary tree traversal-- beadth-first and depth-first【1月23日学习笔记】

//Binary tree traversal-- beadth-first and depth-first
#include<iostream>
#include<queue>//STL
using namespace std;

struct node {
    int data;
    node *left, *right;
};

node* getnewnode(int x)
{
    node* temp = new node;
    temp->data = x;
    temp->left = temp->right = NULL;

    return temp;
}

void insert(node*& travptr, int data) {//Node*& travptr 表示 travptr 是一个引用，引用的是一个指向 Node 类型的指针

    if (travptr == NULL)
    {
        travptr = getnewnode(data);
        return;
    }
    (data > travptr->data) ? insert(travptr->right, data) : insert(travptr->left, data);
}

//先根遍历
void preorder(node* root) {
    if (root == NULL)  return;//既是特殊情况，又是中止情况
    cout << root->data << " ";
    preorder(root->left);
    preorder(root->right);
}//空间复杂度：O（h）where h is the height of the tree

//中根遍历
void inorder(node* root) {
    if (root == NULL)  return;
    inorder(root->left);
    cout << root->data << " ";
    inorder(root->right);
}//空间复杂度：O（h）where h is the height of the tree

//后根遍历
void postorder(node* root) {
    if (root == NULL)  return;
    postorder(root->left);
    postorder(root->right);
    cout << root->data << " ";
}//空间复杂度：O（h）where h is the height of the tree

int main()
{
    node* root = NULL;

    insert(root, 2);
    insert(root, 1);
    insert(root, 3);
    insert(root, 0);
    insert(root, 5);
    preorder(root);   cout << endl;
    inorder(root);      cout << endl;
    postorder(root);     cout << endl;
    return 0;
}