学步园

非递归用栈实现先序遍历

#include <iostream>
#include <vector>
#include <stack> 
using namespace std;

struct TreeNode 
{
	int val;
	TreeNode *left;
	TreeNode *right;
    TreeNode(int x) : val(x), left(NULL), right(NULL) {}
};

stack<TreeNode*> st;
class Solution {
public:
    vector<int> preorderTraversal(TreeNode *root) {
    	vector<int> v;
    	TreeNode *p;
	    while(root || !st.empty())
        {
        	while(root)
        	{
        		v.push_back(root->val);
        		st.push(root);
	        	root = root->left;
	        }
	        if(!st.empty())
	        {
        		root = st.top();st.pop();
        	}
        	root = root->right;
        }
        return v;
    }
};

int main(void)
{
	Solution s;

	/*
TreeNode *root = new TreeNode(1);
	TreeNode *node1 = new TreeNode(2);  root->right = node1;
	TreeNode *node2 = new TreeNode(3);  node1->left = node2;*/
	
/*
	TreeNode *root = new TreeNode(1);
	TreeNode *node1 = new TreeNode(4);  root->left = node1;
	TreeNode *node2 = new TreeNode(3);  root->right = node2;
	TreeNode *node3 = new TreeNode(2);  node1->left = node3;*/
	
/*
	TreeNode *root = new TreeNode(3);
	TreeNode *node2 = new TreeNode(1);  root->right = node2;
	TreeNode *node3 = new TreeNode(2);  node2->left = node3;*/
	
	TreeNode *root = new TreeNode(2);
	TreeNode *node1 = new TreeNode(1);  root->left = node1;
	TreeNode *node2 = new TreeNode(3);  root->right = node2;
	TreeNode *node3 = new TreeNode(4);  node1->right = node3;
	
	vector<int> re = s.preorderTraversal(root);
	
	vector<int>::iterator iter;
	for(iter = re.begin(); iter != re.end(); ++iter)
	{
		cout << *iter << endl;
	}
	
	return 0;
}