2

Author: kedebug

BinaryTreeInorderTraversal/BinaryTreeInorderTraversal.cpp

@@ -0,0 +1,68 @@
+/**
+ * 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) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        vector<int> inorder;
+        stack<TreeNode*> tree_stack;
+        TreeNode *node = root;
+        
+        while (node || !tree_stack.empty()) {
+            while (node) {
+                tree_stack.push(node);
+                node = node->left;
+            }
+            if (!tree_stack.empty()) {
+                node = tree_stack.top();
+                tree_stack.pop();
+                inorder.push_back(node->val);
+                node = node->right;
+            }
+        }
+        return inorder;
+    }
+};
+
+// solution 2, O(1) space
+class Solution {
+public:
+    vector<int> inorderTraversal(TreeNode *root) {
+        // Start typing your C/C++ solution below
+        // DO NOT write int main() function
+        
+        vector<int> inorder;
+        TreeNode *current = root;
+        
+        while (current != NULL) {
+            if (current->left == NULL) {
+                inorder.push_back(current->val);
+                current = current->right;
+            }
+            else {
+                TreeNode *prev = current->left;
+                while (prev->right && prev->right != current)
+                    prev = prev->right;
+                if (prev->right == NULL) {
+                    prev->right = current;
+                    current = current->left;
+                }
+                else {
+                    inorder.push_back(current->val);
+                    prev->right = NULL;
+                    current = current->right;
+                }
+            }
+        }
+        return inorder;
+    }
+};