leetcode144-binary-tree-preorder-traversal_recursive2.cpp

#include<stack>
#include<vector>
#include<algorithm>
#include<iostream>
usingnamespacestd;
/**
 * Definition for a binary tree node.
*/
structTreeNode {
int val;
 TreeNode *left;
 TreeNode *right;
TreeNode() : val(0), left(nullptr), right(nullptr) {}
TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
};

/* 前序遍历顺序: 根 左 右 */
classSolution {
public:
 vector<int> preorderTraversal(TreeNode* root) {
if(root == NULL)
return {};

 vector<int> res;
 res.push_back(root->val);
 vector<int> left = preorderTraversal(root->left);
 vector<int> right = preorderTraversal(root->right);
// 合并各个数组到res数组
 res.insert(res.end(), left.begin(), left.end());
 res.insert(res.end(), right.begin(), right.end());

return res; 
 }
};

// Test
intmain()
{
 Solution sol;

 TreeNode* root = newTreeNode(1);
 root->left = NULL;
 root->right = newTreeNode(2);
 root->right->left = newTreeNode(3);

 vector<int> res = sol.preorderTraversal(root);
for (auto num : res)
 cout << num << endl; 

return0;
}