每日一刷

二叉树

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实现二叉树先序，中序和后序遍历

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一、题目描述

二、解题步骤

/**
 * 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<>>
     */
    void firstOrder(vector<int> &res1, TreeNode* root) {
        if (root != NULL) {
            res1.push_back(root->val);
            
            firstOrder(res1, root->left);
            
            firstOrder(res1, root->right);
        }
    }
    
    void secondOrder(vector<int> &res2, TreeNode* root) {
        if (root != NULL) {
            
            secondOrder(res2, root->left);
            
            res2.push_back(root->val);
          
            secondOrder(res2, root->right);
        }
    }
    
    void thirdOrder(vector<int> &res3, TreeNode* root) {
        if (root != NULL) {
           
            thirdOrder(res3, root->left);
            
           
            thirdOrder(res3, root->right);
            
            res3.push_back(root->val);
        }
    }
    
    vector<vector<int> > threeOrders(TreeNode* root) {
        // write code here
        vector<vector<int>> res;
        vector<int> res1;
        firstOrder(res1, root);
        res.push_back(res1);
        
        vector<int> res2;
        secondOrder(res2, root);
        res.push_back(res2);
        
        vector<int> res3;
        thirdOrder(res3, root);
        res.push_back(res3);
        
        return res;
    }
};
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