二叉树的前序遍历

思路：小心程序运行栈溢出，用stack模拟

class Solution {
public:
    vector<int> preorderTraversal(TreeNode *root) {
        stack<TreeNode*> stk;
        vector<int> res;
        if (root)
            stk.push(root);
        else
            return res;
        TreeNode* tmpNode;
        while (!stk.empty())
        {
            tmpNode = stk.top();
            res.push_back(tmpNode->val);
            stk.pop();
            if (tmpNode->right !=NULL){
                stk.push(tmpNode->right);
            }
            if (tmpNode->left != NULL){
                stk.push(tmpNode->left);
            }
        }
        return res;
    }
};

Binary Tree Preorder Traversal

原文：http://www.cnblogs.com/flyjameschen/p/2afc00fa85d8bef10d50fd962bd07c2e.html