【树】leetcode_94_二叉树的中序遍历

【树】leetcode_94_二叉树的中序遍历

c++迭代，

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
        vector<int> result;
        stack<TreeNode*> re;
        while(root!=nullptr || !re.empty()){
            while(root!=nullptr){
                re.push(root);
                root = root->left;
            }

            if(!re.empty()){
                root = re.top();

                result.push_back(root->val);
                re.pop();

                root=root->right;
            }
        }
        return  result;
    }
};

递归

/**
 * Definition for a binary tree node.
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode() : val(0), left(nullptr), right(nullptr) {}
 *     TreeNode(int x) : val(x), left(nullptr), right(nullptr) {}
 *     TreeNode(int x, TreeNode *left, TreeNode *right) : val(x), left(left), right(right) {}
 * };
 */
class Solution {
public:
    vector<int> inorderTraversal(TreeNode* root) {
         vector<int> re;
         get_re(root,re);
         return(re);
    }
    void get_re(TreeNode *root, vector<int> &re){
        if (root == nullptr){
            return;
        }
        get_re(root->left,re);
        re.push_back(root->val);
        get_re(root->right,re);

    }
};