Leetcode-144. 二叉树的前序遍历

/**
 * 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 {
    vector<int> fNum;
public:
    vector<int> preorderTraversal(TreeNode* root) {
        init();
        fDfs(root);
        return fNum;
    }
    void fDfs(TreeNode* root)
    {
        if (root!= NULL)
        {
            fNum.push_back(root->val);
            fDfs(root->left);  //遍历左子树
            fDfs(root->right);  //遍历右子树
        }
    }
    void init()
    {
        fNum.clear();
    }
};