LeetCode: Binary Tree Preorder Traversal [144]

標籤：leetcode   演算法   面試   

【題目】

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?

【題意】

    非遞迴返回先序遍曆結果

【思路】

        維護一個棧即可

【代碼】

/** * Definition for binary tree * 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> result;        stack<TreeNode*> st;        TreeNode*node=root;        while(node){            result.push_back(node->val);            st.push(node);            node=node->left;        }        while(!st.empty()){            node=st.top()->right; st.pop();            while(node){                result.push_back(node->val);                st.push(node);                node=node->left;            }        }        return result;    }};