tree.cpp

#include <iostream>
#include <vector>
#include <string>
#include <algorithm>
#include <cstdio>
#include <stack>
using namespace std;
struct TreeNode {
	int val;
	TreeNode *left;
	TreeNode *right;
	TreeNode(int x) : val(x), left(nullptr), right(nullptr){}
};
class Solution {
public:
	vector<int> preorderTraversal(TreeNode *root) {
		vector<int> result;
		if (root == NULL)
			return result;
		stack<TreeNode *>s;
		s.push(root);
		while (!s.empty()) {
			TreeNode *p = s.top();
			s.pop();
			result.push_back(p->val);
			if (p->right)
				s.push(p->right);
			if (p->left)
				s.push(p->left);
		}
		return result;
	}
};
TreeNode *mk_node(int val)
{
	return new TreeNode(val);
}
TreeNode *mk_child(TreeNode *root, TreeNode *left, TreeNode *right)
{
	root->left = left;
	root->right = right;
	return root;
}
TreeNode *mk_child(TreeNode *root, int left, int right)
{
	return mk_child(root, new TreeNode(left), new TreeNode(right));
}
TreeNode *mk_child(int root, int left, int right)
{
	return mk_child(new TreeNode(root), new TreeNode(left), new TreeNode(right));
}
int main(int argc, char **argv)
{
	Solution solution;
	TreeNode *root = mk_child(10,5,15);
	mk_child(root->right, 6, 20);
	mk_child(root->left, 2, 3);
	auto result = solution.preorderTraversal(root);
	for_each(result.begin(), result.end(), [](int i){cout << i << " ";});
	cout << endl;
	return 0;
}