【手撕代码2】-二叉树中序遍历（递归/非递归）

1.递归

2.非递归的核心在于使用栈的先进后出

#include<cstdio>
#include<iostream>
#include<stack>
using namespace std;

struct treenode
{
    int val;
    treenode* left;
    treenode* right;
};

//递归
void inorder(treenode *root)
{
    if (root!=NULL)return;
    inorder(root->left);
    cout << root->val<<" ";
    inorder(root->right);

}
//非递归
void inorder2(treenode* root)
{
    stack<treenode*> a;
    a.push(root);
    treenode* t=root->left;
    while (t != NULL||!a.empty()) {
        while (t != NULL)
        {
            a.push(t);
            t = t->left;
        }
        if(!a.empty())
        {
            t = a.top();
            cout << t->val<<" ";
            a.pop();
            if (t->right != NULL)a.push(t->right);
        }
    }

}
int main()
{
    treenode* root;
    inorder(root);
    inorder2(root);
    
    return 0;
}

详见 https://blog.csdn.net/czy47/article/details/81254984