题解 | #实现二叉树先序，中序和后序遍历#

直接遍历，定义三个数组

class Solution {
public:
    /**
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    vector<int> nums1;
    vector<int> nums2;
    vector<int> nums3;
    void TravelNode(TreeNode* root){
        if(root==nullptr)  return;
        nums1.push_back((root->val));
        FirstOrder(root->left);
        nums2.push_back((root->val));
        FirstOrder(root->right);
        nums3.push_back((root->val));
    }

    vector<vector<int> > threeOrders(TreeNode* root) {
        vector<vector<int>> vec;
        TravelNode(root);
        vec.push_back(nums1);
        vec.push_back(nums2);
        vec.push_back(nums3);
        return vec;
    }
};