二叉树-前中后序遍历-简单

描述

给出一棵二叉树，返回其节点值的前中后序遍历。

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样例

给出一棵二叉树 {1,#,2,3},

前序遍历程序

/**
 * Definition of TreeNode:
 * class TreeNode {
 * public:
 *     int val;
 *     TreeNode *left, *right;
 *     TreeNode(int val) {
 *         this->val = val;
 *         this->left = this->right = NULL;
 *     }
 * }
 */

class Solution {
public:
    /**
     * @param root: A Tree
     * @return: Preorder in ArrayList which contains node values.
     */
    vector<int> res;
    void traverse(TreeNode *root){
        if(root == NULL)
            return;
        res.push_back(root->val);
        traverse(root->left);
        traverse(root->right);
    }
    vector<int> preorderTraversal(TreeNode * root) {
        // write your code here
        //res.clear();
        traverse(root);
        return res;
    }
};

中序遍历程序

class Solution {
public:
    /**
     * @param root: A Tree
     * @return: Inorder in ArrayList which contains node values.
     */
    vector<int> res;
    void traverse(TreeNode *root){
        if(root == NULL)
            return;
        traverse(root->left);
        res.push_back(root->val);
        traverse(root->right);
    }
    vector<int> inorderTraversal(TreeNode * root) {
        // write your code here
        //res.clear();
        traverse(root);
        return res;
    }
};

后序遍历程序

class Solution {
public:
    /**
     * @param root: A Tree
     * @return: Postorder in ArrayList which contains node values.
     */
    vector<int> res;
    void traverse(TreeNode *root){
        if(root == NULL)
            return;
        traverse(root->left);
        traverse(root->right);
        res.push_back(root->val);
    }
    vector<int> postorderTraversal(TreeNode * root) {
        // write your code here
        traverse(root);
        return res;
    }
};