Given a binary tree, return the inorder traversal of its nodes' values. http://www.leetcode.com/onlinejudge

inorder_traversal_iterative.cpp

#include <stack>
using namespace std;

/**
 * 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> inorderTraversal(TreeNode *root) {
        vector<int> ret;
        if (root == NULL) {
            return ret;
        }
        stack<TreeNode*> s;
        TreeNode* cur = root;
        while (!s.empty() || cur != NULL) {
            if (cur == NULL) {
                cur = s.top();
                ret.push_back(cur->val);
                s.pop();
                cur = cur->right;
            }
            else {
                s.push(cur);
                cur = cur->left;
            }
        }
        return ret;
    }
};

leetcode_binary_tree_inorder_traversal.cpp

/**
 * 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> inorderTraversal(TreeNode *root) {
        vector<int> ret;
        if (root == NULL) {
            return ret;
        }
        vector<int> left = inorderTraversal(root->left);
        vector<int> right = inorderTraversal(root->right);
        ret.insert(ret.end(), left.begin(), left.end());
        ret.push_back(root->val);
        ret.insert(ret.end(), right.begin(), right.end());
        return ret;
    }
};