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;
 *	TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 * };
 */
#include <vector>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param root TreeNode类 the root of binary tree
     * @return int整型vector<vector<>>
     */
    
    void inorder(TreeNode *root,vector<int> &a){
        if(root==nullptr){
            return  ;
        }
        else{
            
            inorder(root->left, a);
            a.push_back(root->val);//先存进去
            inorder(root->right, a);
        }


    }
    void preorder(TreeNode *root,vector<int> &a){
        if(root==nullptr){
            return  ;
        }
        else{  
            a.push_back(root->val);//先存进去
            preorder(root->left, a);
            preorder(root->right, a);
        }


    }
    void postorder(TreeNode *root,vector<int> &a){
        if(root==nullptr){
            return  ;
        }
        else{       
            postorder(root->left, a);
            postorder(root->right, a);
            a.push_back(root->val);//先存进去
        }


    }


    vector<vector<int> > threeOrders(TreeNode* root) {
        vector<vector<int>> res(3);
        preorder(root, res[0]);
        inorder(root, res[1]);
        postorder(root, res[2]);
       

        return res;
        // write code here
 
        
    }
};

动态数组最好先初始化给个值申请空间