Cinte's Leetcode Record
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144. 二叉树的前序遍历

Posted on Edited on In Disqus:
Symbols count in article: 1.3k Reading time ≈ 1 mins.

144. 二叉树的前序遍历

迭代算法

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
        stack<TreeNode*> q;
        vector<int> ret;
        while(!q.empty() || root)
        {
            while(root)
            {
                q.push(root);
                ret.push_back(root->val);
                root = root->left;
            }
            root = q.top();
            q.pop();
            root = root->right;
        }
        return ret;
    }
};

递归

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/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> preorderTraversal(TreeNode* root) {
        tra(root);
        return ret;
    }
private:
    vector<int> ret;
    void tra(TreeNode* root)
    {
        if(!root)
            return;
        ret.push_back(root->val);
        tra(root->left);
        tra(root->right);
    }
};