94. 二叉树的中序遍历
给定一个二叉树，返回它的中序 遍历。
示例:
输入: [1,null,2,3]
1
2
/
3
输出: [1,3,2]
递归解法：
/*
* @lc app=leetcode.cn id=94 lang=cpp
*
* [94] 二叉树的中序遍历
*/
// @lc code=start
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> inorderTraversal(TreeNode* root) {
vector<int> ans;
inorder(root, ans);
return ans;
}
void inorder(TreeNode *root, vector<int>& ans) {
if (root == nullptr) {
return;
}
inorder(root->left, ans);
ans.push_back(root->val);
inorder(root->right, ans);
}
};
迭代写法：
/*
* @lc app=leetcode.cn id=94 lang=cpp
*
* [94] 二叉树的中序遍历
*/
// @lc code=start
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
vector<int> inorderTraversal(TreeNode* root) {
// 方法二：迭代
stack<TreeNode*> S;
vector<int> v;
TreeNode *rt = root;
while (rt || S.size())
{
while (rt) {
S.push(rt);
rt = rt->left;
}
rt = S.top(); S.pop();
v.push_back(rt->val);
rt = rt->right;
}
return v;
}
};
// @lc code=end