二叉树的遍历

二叉树的前序遍历

给出一棵二叉树，返回其节点值的前序遍历。

样例

给出一棵二叉树 {1,#,2,3},

   1    \     2    /   3

 返回 [1,2,3].

解题思路：利用递归的思想

/** * Definition of TreeNode: * class TreeNode { * public: *     int val; *     TreeNode *left, *right; *     TreeNode(int val) { *         this->val = val; *         this->left = this->right = NULL; *     } * } */class Solution {public:    /**     * @param root: The root of binary tree.     * @return: Preorder in vector which contains node values.     */    vector<int>result;    void preorderTemp(TreeNode *root)    {        if (root == NULL)        {            return;        }        result.push_back(root->val);        preorderTemp(root->left);        preorderTemp(root->right);    }    vector<int> preorderTraversal(TreeNode *root) {        // write your code here        preorderTemp(root);        return result;    }    };