题解 | #实现二叉树先序，中序和后序遍历#

/**
 * struct TreeNode {
 *    int val;
 *    struct TreeNode *left;
 *    struct TreeNode *right;
 * };
 */

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
     vector<vector<int> >a;
     void Preorder(TreeNode*root){
         if(root!=NULL){
         cout<<root->val<<' ';
         a[0].push_back(root->val);
         Preorder(root->left);
         Preorder(root->right);
         }
     }
     void InOrder(TreeNode*root){
         if(root!=NULL){

         InOrder(root->left);
         cout<<root->val<<' ';
         a[1].push_back(root->val);
         InOrder(root->right);
         }
     }
     void BackOder(TreeNode*root){
         if(root!=NULL){

         BackOder(root->left);
         BackOder(root->right);
         cout<<root->val<<' ';
         a[2].push_back(root->val);
         }
     }
    vector<vector<int> > threeOrders(TreeNode* root) {
        a.resize(3);
        // write code here
        Preorder(root);
        cout<<endl;
        InOrder(root);
        cout<<endl;
        BackOder(root);
        return a;
    }
};