leetcode/Binary_Tree_Inorder_Traversal.cpp at master · whodewho/leetcode · GitHub

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/**
 * Definition for binary tree
 * struct TreeNode {
 *     int val;
 *     TreeNode *left;
 *     TreeNode *right;
 *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
 * };
 */
//O(N)
//O(N)

class Solution {
    public:
        vector<int> inorderTraversal(TreeNode *root) {
            // Start typing your C/C++ solution below
            // DO NOT write int main() function
            vector<int> res;
            worker(root,res);
            return res;
        }

        void worker(TreeNode* root,vector<int> &vec)
        {
            if(root==NULL)return;
            worker(root->left,vec);
            vec.push_back(root->val);
            worker(root->right,vec);
        }

        vector<int> inorderTraversal(TreeNode *node) {
            vector<int> result;
            if (node == NULL) return result;
            stack<TreeNode*> stk;
            TreeNode* curr = node;
            while (!stk.empty() || curr != NULL) {
                if (curr != NULL) {
                    stk.push(curr);
                    curr = curr->left;
                }
                else {
                    curr = stk.top();
                    stk.pop();
                    result.push_back(curr->val);
                    curr = curr->right;
                }
            }
            return result;
        }

        vector<int> postorderTraversal(TreeNode *root) {
            vector<int> result;
            if(!root)return result;
            stack<TreeNode*> stk;
            while(!stk.empty()||root!=NULL)
            {
                if(root)
                {
                    stk.push(root);
                    root=root->left;
                }
                else
                {
                    TreeNode* tmp=stk.top();
                    if(!(tmp->right)||!result.empty()&&result[result.size()-1]==tmp->right->val)
                    {
                        result.push_back(tmp->val);
                        stk.pop();
                    }
                    else
                    {
                        root=tmp->right;
                    }
                }
            }
            return result;
        }

        vector<int> preorderTraversal(TreeNode *node)
        {
            vector<int> result;
            if(node==NULL)return result;
            stack<TreeNode *>stk;
            stk.push(node);
            while(!stk.empty())
            {
                TreeNode* curr=stk.top();
                stk.pop();
                result.push_back(curr);
                if(curr->right)
                    stk.push(curr->right);
                if(curr->left)
                    stk.push(curr->left);
            }
        }
};