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  • [LeetCode]Binary Tree Preorder Traversal

    题目描述:(链接

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

    For example:
    Given binary tree {1,#,2,3},

       1
        
         2
        /
       3
    

    return [1,2,3].

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

    解题思路:

    迭代版:

     1 /**
     2  * Definition for a binary tree node.
     3  * struct TreeNode {
     4  *     int val;
     5  *     TreeNode *left;
     6  *     TreeNode *right;
     7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     8  * };
     9  */
    10 class Solution {
    11 public:
    12     vector<int> preorderTraversal(TreeNode* root) {
    13         vector<int> result;
    14         stack<TreeNode *> cache;
    15         TreeNode *p = root;
    16         if (p != nullptr) {
    17             cache.push(p);
    18         }
    19         
    20         while (!cache.empty()) {
    21             p = cache.top();
    22             cache.pop();
    23             result.push_back(p->val);
    24             
    25             if (p->right != nullptr) {
    26                 cache.push(p->right);
    27             }
    28             
    29             if (p->left != nullptr) {
    30                 cache.push(p->left);
    31             }
    32         }
    33         
    34         return result;
    35     }
    36 };

     递归版:

     1 /**
     2  * Definition for a binary tree node.
     3  * struct TreeNode {
     4  *     int val;
     5  *     TreeNode *left;
     6  *     TreeNode *right;
     7  *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
     8  * };
     9  */
    10 class Solution {
    11 public:
    12     vector<int> preorderTraversal(TreeNode* root) {
    13         if (root != nullptr) {
    14             result.push_back(root->val);
    15             preorderTraversal(root->left);
    16             preorderTraversal(root->right);
    17         }
    18         
    19         return result;
    20     }
    21 private:
    22     vector<int> result;
    23 };
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  • 原文地址:https://www.cnblogs.com/skycore/p/4986124.html
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