标签：des style blog http io color ar os sp
Given a binary tree, return the preorder traversal of its nodes‘ values.
For example:
Given binary tree {1,#,2,3},
1
2
/
3
return [1,2,3].
Note: Recursive solution is trivial, could you do it iteratively?
这题简单，属于课本习题的难度，题目提示说用迭代试试，当然用递归也可以AC的。迭代的时候要注意栈的性质，不要push反了。
void preorderIter2(TreeNode *node, stack<TreeNode*>&st, vector<int>&ret) { while (!st.empty()) { TreeNode *top = st.top(); st.pop(); ret.push_back(top->val); if (top->right) st.push(top->right); if (top->left) st.push(top->left); } } vector<int> preorderTraversal(TreeNode *root) { vector<int> ret; if (!root) return ret; stack<TreeNode *> st; st.push(root); preorderIter2(root, st, ret); return ret; }
迭代版
void preorderIter(TreeNode *node, vector<int> &ret) { if (!node) return; ret.push_back(node->val); cout << node->val <<endl; preorderIter(node->left, ret); preorderIter(node->right, ret); }
[LeetCode] Binary Tree Preorder Traversal
标签：des style blog http io color ar os sp
原文地址：http://www.cnblogs.com/agentgamer/p/4080404.html
