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<int> first;
    vector<int> mid;
    vector<int> last;
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        firstorder(root);
        midorder(root);
        lastorder(root);
        vector<vector<int>> threeorders;
        threeorders.push_back(first);
        threeorders.push_back(mid);
        threeorders.push_back(last);
        return threeorders;
    }
    void firstorder(TreeNode *root){
        if(root!=NULL){
        first.push_back(root->val);
        if(root->left!=NULL) firstorder(root->left);
        if(root->right!=NULL) firstorder(root->right);
        }
        return;
    }
    void midorder(TreeNode *root){
        if(root!=NULL){
        if(root->left!=NULL) midorder(root->left);
        mid.push_back(root->val);
        if(root->right!=NULL) midorder(root->right);
        }
        return;
    }
    void lastorder(TreeNode *root){
        if(root!=NULL){
        if(root->left!=NULL) lastorder(root->left);
        if(root->right!=NULL) lastorder(root->right);
        last.push_back(root->val);
        }
        return;
    }
};