94. Binary Tree Inorder Traversal

二叉树中序遍历

最新推荐文章于 2021-09-23 07:24:48 发布

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本文介绍了一种算法，用于实现二叉树的中序遍历，包括递归和迭代两种方法。递归方法直观易懂，而迭代方法则使用栈来避免递归调用。文章提供了完整的代码实现。

94. Binary Tree Inorder Traversal

Medium

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Given a binary tree, return the inorder traversal of its nodes' values.

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,3,2]

Follow up: Recursive solution is trivial, could you do it iteratively?

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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 {//递归算法
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> in;
        inorder(root,in);
        return in;
    }
    void inorder(TreeNode* root,vector<int>& in){
        if(root==NULL) return;
        inorder(root->left,in);
        in.push_back(root->val);
        inorder(root->right,in);
    }
};

/**
 * 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 {//迭代算法
public:
    vector<int> inorderTraversal(TreeNode* root) {
    	vector<int> in;
        if(root==NULL) return in;
        TreeNode* cur=root;
        stack<TreeNode*> st;
        while(st.empty()==false||cur!=NULL){
        	while(cur!=NULL){
        		st.push(cur);
        		cur=cur->left;
        	}
        	cur=st.top();
        	st.pop();
        	in.push_back(cur->val);
        	cur=cur->right;
        }
        return in;
    }
};