LeetCode Binary Tree Preorder Traversal

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1.题目

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?

2.解决方案1

class Solution { 
public: 
    vector<int> preorderTraversal(TreeNode *root) { 
        vector<int> ans; 
        deque<TreeNode*> node_list; 
        if(root == NULL) return ans; 
        node_list.push_front(root); 
        while(!node_list.empty()) 
        { 
            TreeNode *cur = node_list.back(); 
            node_list.pop_back(); 
            ans.push_back(cur -> val); 
            if(cur -> right != NULL) node_list.push_back(cur -> right); 
            if(cur -> left != NULL) node_list.push_back(cur -> left); 
        } 
         
        return ans; 
    } 
};

3.解决方案2

class Solution {
public:
    vector<int> path;
    void preorder(TreeNode *root){
        if(!root)
           return;
        path.push_back(root->val);
        //if(root->left)
          preorder(root->left);
        //if(root->right)
          preorder(root->right);
    }
    vector<int> preorderTraversal(TreeNode *root) {
        preorder(root);
        return path;
    }
};

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LeetCode Binary Tree Preorder Traversal

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原文地址：http://blog.csdn.net/fox64194167/article/details/44100695