Leetcode.94.二叉树的中序遍历

Posted 2021-03-15 黄栋

94.二叉树的中序遍历

递归遍历

迭代遍历

/**
 * 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) {
        stack<TreeNode*> lt;
        vector<int> ans;
        TreeNode* curr = root;
        while(!lt.empty() || curr!=nullptr){
            while(curr != nullptr){
                lt.push(curr);
                curr=curr->left;
            }
            TreeNode* p = lt.top();
            lt.pop();
            ans.push_back(p->val);
            if(p->right != nullptr)
            {
                curr = p->right;
            }
        }
        return ans;
    }
};

莫里斯遍历

莫里斯遍历主要思想是将中间根节点放到左子树的最右侧节点。
可以从运行时间和使用内存看出来，确实莫里斯遍历要由于普通迭代。

/**
 * 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;
        TreeNode* curr=root;
        while(curr!=nullptr)
        {
            if(curr->left == nullptr){
                ans.push_back(curr->val);
                curr=curr->right;
            }
            else{
                TreeNode* p = curr->left;
                while(p->right!=nullptr){
                    p=p->right;
                }
                p->right= curr;
                TreeNode* t=curr;
                curr = curr->left;
                t->left = nullptr;
            }
        }
        return ans;
    }
};