二叉树的 前序 || 中序 || 后序遍历

直奔代码：

///前序遍历：先遍历根节点，再遍历左子树，最后遍历右子树
/*
#include <bits/stdc++.h>
using namespace std;

struct tree
{
    struct tree *left;
    int date;
    struct tree *right;
};
typedef struct tree treenode;
typedef struct tree * b_tree;

b_tree add(b_tree root, int node)    ///插入结点+
{
    b_tree newnode;
    b_tree currentnode;
    b_tree parentnode;

    newnode = (b_tree)malloc(sizeof(treenode));
    newnode->date = node;
    newnode->left = NULL;
    newnode->right = NULL;

    if(root == NULL)         ///第一个结点建立
        return newnode;
    else
    {
        currentnode = root; ///储存当前结点
        while(currentnode != NULL)     ///当前结点不为空
        {
            parentnode = currentnode;  ///储存父结点
            if(currentnode->date > node)
                currentnode = currentnode->left;  ///左子树
            else
                currentnode = currentnode->right; ///右子树
        }
        if(parentnode->date > node)
            parentnode->left = newnode;
        else
            parentnode->right = newnode;
    }
    return root;
}

b_tree create(int *data, int len)
{
    int i;
    b_tree root = NULL;
    for(int i = 1; i <= len; i++)
    {
        root = add(root, data[i]);
    }
    return root;
}

void print(b_tree root)
{
    if(root != NULL)
    {
        cout << root->date << ' ';
        print(root->left);
        print(root->right);
    }
}

int main()
{
    int N;
    b_tree root = NULL;
    cin >> N;
    int node[N+1];
    for(int i = 1; i <= N; i++)
        cin >> node[i];
    root = create(node, N);
    print(root);
    cout << endl;
    return 0;
}
*/


///中序遍历：先遍历左子树，再遍历根结点，最后才遍历右子树
/*
void print(b_tree root)
{
    if(root != NULL)
    {
        print(root->left);
        cout << root->date << ' ';
        print(root->right);
    }
}
*/

///后序遍历：先遍历左子树，再遍历右子树，最后才遍历根结点
/*
void print(b_tree root)
{
    if(root != NULL)
    {
        print(root->left);
        print(rooy->right);
        cout << root->date << ' ';
    }
}
*/