leetcode 94. Binary Tree Inorder Traversal

相关问题

144. Binary Tree Preorder Traversal
94. Binary Tree Inorder Traversal
145. Binary Tree Postorder Traversal

Discription

Given a binary tree, return the inorder traversal of its nodes’ values.

For example:
Given binary tree {1,#,2,3},
1
  \
    2
  /
3
return [1,2,3].

思路

每次都向左走到头，然后再向右走，如图：

时间复杂度：?
空间复杂度：?

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> inorderTraversal(TreeNode* root) {        vector<TreeNode*> sta;        vector<int> res;        if (root) sta.push_back(root);        while (!sta.empty())        {            // 向左走到头            while (sta.back()) sta.push_back(sta.back()->left);            // 弹出空指针            sta.pop_back();            if (!sta.empty())            {                TreeNode *pNode = sta.back();                sta.pop_back();                res.push_back(pNode->val);  // 和先序遍历不同之处在于返回时（弹出时）访问                sta.push_back(pNode->right);            }        }        return res;    }};