94. Binary Tree Inorder Traversal.cpp

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

Example:

Input: [1,null,2,3]
   1
    \
     2
    /
   3

Output: [1,3,2]
Follow up: Recursive solution is trivial, could you do it iteratively?




/**
 * 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> v;
        if(!root) return v;
        TreeNode* p=root;
        stack<TreeNode*>s;
        while(1){
            while(p){
                s.push(p);
                p=p->left;
            }
            if(s.empty()) break;
            p=s.top();
            s.pop();
            v.push_back(p->val);
            p=p->right;
        }
        return v;
    }
};