leetcode-94-Binary Tree Inorder Traversal

                                                                                                       

Binary Tree Preorder Traversal

 

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].

/** * 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 {  //先序遍历  非递归public:    vector<int> preorderTraversal(TreeNode* root) {           vector<int>v;           v.clear();           stack<TreeNode*>s;           TreeNode* x;           s.push(root);           if(!root) return v;           while(!s.empty()){               x=s.top();               v.push_back(x->val);               s.pop();               if(x->right) s.push(x->right);               if(x->left) s.push(x->left);           }           return v;    }};class Solution { //先序遍历  递归public:    vector<int>v;    vector<int> preorderTraversal(TreeNode* root) {        v.clear();        if(!root) return v;        pre(root);        return v;    }    void pre(TreeNode* p){        if(!p) return;        v.push_back(p->val);        pre(p->left);        pre(p->right);    }};