Leetcode 94. Binary Tree Inorder Traversal

发表于 | 分类于

https://leetcode.com/problems/binary-tree-inorder-traversal/

二叉树的中序遍历

递归：

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/**
 * 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> res;
    
    vector<int> inorderTraversal(TreeNode* root) {
        if(root != NULL){
            inorderTraversal(root->left);
            res.push_back(root->val);
            inorderTraversal(root->right);
        }
        
        return res;
    }
};

非递归：

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/**
 * 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> res;
        stack<TreeNode*> tempStack;
        while(!tempStack.empty() || root != NULL){
            if(root != NULL){
                tempStack.push(root);
                root = root->left;
            }
            else{
                root = tempStack.top();
                res.push_back(tempStack.top()->val);
                tempStack.pop();
                root = root->right;
            }
        }
        
        return res;
    }
};

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