Binary Tree Preorder Traversal问题及解法
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问题描述:
Given a binary tree, return the preorder traversal of its nodes' values.
示例:
Given binary tree {1,#,2,3}
,
1 \ 2 / 3
return [1,2,3]
.
问题分析:
我们知道,递归方法是借助栈来实现保存参数的。这里如果我们要用迭代方法来求解,需要设置一个栈来保存各个节点。由于栈是先进后出的数据结构,再加上这是先序遍历的题目,所以存放结点时先放右结点,再放左结点。
过程详见代码:
/** * Definition for a binary tree node. * struct TreeNode { * int val; * TreeNode *left; * TreeNode *right; * TreeNode(int x) : val(x), left(NULL), right(NULL) {} * }; */class Solution {public: vector<int> preorderTraversal(TreeNode* root) { vector<int> res; if (!root) { return res; } stack<TreeNode *> treeStack; treeStack.push(root); while(!treeStack.empty()) { TreeNode *temp = treeStack.top(); res.push_back(temp->val); treeStack.pop(); if (temp->right) { treeStack.push(temp->right); } if (temp->left) { treeStack.push(temp->left); } } return res; }};
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