LeetCode: 617 solved (3 solutions)

Author: devMEremenko

Python/LeetCode/617. Merge Two Binary Trees.py

@@ -2,25 +2,30 @@
 
 # Definition for a binary tree node.
 class TreeNode:
-    def __init__(self, x):
-        self.val = x
-        self.left = None
-        self.right = None
+    def __init__(self, val=0, left=None, right=None):
+        self.val = val
+        self.left = left
+        self.right = right
 
 from collections import deque
 
 class Solution:
 
-    def solve_recursively_new_tree(self, t1: TreeNode, t2: TreeNode) -> TreeNode:
-        if t1 and t2:
-            root = TreeNode(t1.val + t2.val)
-            root.left = self.solve_recursively_new_tree(t1.left, t2.left)
-            root.right = self.solve_recursively_new_tree(t1.right, t2.right)
-            return root
-        else:
-            return t1 or t2
+    def mergeTrees(self, t1, t2):
+        # return self.solution1_recursive_inplace(t1, t2)
+        # return self.solution2_iterative_inplace(t1, t2)
+        return self.solution3_iterative_using_new_tree(t1, t2)
+        
+    # Time O(min(n, m))
+    def solution1_recursive_inplace(self, t1, t2):
+        if not t1 or not t2: return t1 or t2
+        
+        node = TreeNode(t1.val + t2.val)
+        node.left = self.solution1_recursive_inplace(t1.left, t2.left)
+        node.right = self.solution1_recursive_inplace(t1.right, t2.right)
+        return node
 
-    def solve_iteratively(self, t1: TreeNode, t2: TreeNode) -> TreeNode:
+    def solution2_iterative_inplace(self, t1, t2):
         if not t1 or not t2: return t1 or t2
 
         q = deque()
@@ -29,13 +34,50 @@ def solve_iteratively(self, t1: TreeNode, t2: TreeNode) -> TreeNode:
             v1, v2 = q.popleft()
             v1.val = v1.val + v2.val
 
-            if v1.left and v2.left: q.append([v1.left, v2.left])
-            elif v2.left: v1.left = v2.left #t1.left is None
+            if v1.left and v2.left: 
+                q.append((v1.left, v2.left))
+            elif v2.left: 
+                v1.left = v2.left
 
-            if v1.right and v2.right: q.append([v1.right, v2.right])
-            elif v2.right: v1.right = v2.right #t1.right is None
+            if v1.right and v2.right: 
+                q.append((v1.right, v2.right))
+            elif v2.right: 
+                v1.right = v2.right
         return t1
 
-    def mergeTrees(self, t1: TreeNode, t2: TreeNode) -> TreeNode:
-        # return self.solve_recursively_new_tree(t1, t2)
-        return self.solve_iteratively(t1, t2)
+    def solution3_iterative_using_new_tree(self, t1, t2):
+        
+        def make_tree(node):
+            if not node: return None
+            tree = TreeNode(node.val)
+            tree.left = make_tree(node.left)
+            tree.right = make_tree(node.right)
+            return tree
+        
+        if not t1 or not t2: return make_tree(t1 or t2)
+        
+        res = TreeNode()
+        q = deque()
+        q.append((t1, t2, res))
+        
+        while q:
+            t1, t2, t3 = q.popleft()
+            t3.val = t1.val + t2.val
+            
+            if t1.left and t2.left:
+                t3.left = TreeNode()
+                q.append((t1.left, t2.left, t3.left))
+            elif t1.left:
+                t3.left = make_tree(t1.left)
+            elif t2.left: 
+                t3.left = make_tree(t2.left)
+                
+            if t1.right and t2.right:
+                t3.right = TreeNode()
+                q.append((t1.right, t2.right, t3.right))
+            elif t1.right:
+                t3.right = make_tree(t1.right)
+            elif t2.right: 
+                t3.right = make_tree(t2.right)
+        
+        return res