no message

Author: wuduhren

problems/flatten-binary-tree-to-linked-list.py

@@ -0,0 +1,47 @@
+"""
+Time: O(N)
+Space: O(N)
+
+Pre-Order Traversal
+"""
+class Solution(object):
+    def flatten(self, root):
+        if not root: return None
+        
+        preHead = TreeNode(0)
+        curr = preHead
+        stack = [root]
+        
+        while stack:
+            node = stack.pop()
+            
+            if node.right: stack.append(node.right)
+            if node.left: stack.append(node.left)
+            
+            node.right = None
+            node.left = None
+            curr.right = node
+            curr = curr.right
+            
+        return preHead.right
+
+"""
+Time: O(N)
+Space: O(1)
+
+Morris Traversal
+"""
+class Solution(object):
+    def flatten(self, root):
+        node = root
+        
+        while node:
+            if node.left:
+                rightmost = node.left
+                while rightmost.right: rightmost = rightmost.right
+                rightmost.right = node.right
+                node.right = node.left
+                node.left = None
+            else:
+                node = node.right
+        return root

problems/path-sum-ii.py

@@ -17,4 +17,26 @@ def pathSum(self, root, S):
 """
 Time complexity is O(N), because we traverse all the nodes.
 Space complexity is O(N^2), because in the worst case, all node could carry all the other nodes in the `path`.
-"""
+"""
+
+
+
+"""
+Time complexity is O(N), because we traverse all the nodes.
+Space complexity is O(N^2), because in the worst case, all node could carry all the other nodes in the `path`.
+"""
+class Solution(object):
+    def pathSum(self, root, targetSum):
+        if not root: return []
+        
+        ans = []
+        stack = [(root, root.val, [root.val])]
+        
+        while stack:
+            node, total, path = stack.pop()
+            
+            if not node.left and not node.right and total==targetSum: ans.append(path)
+            if node.left: stack.append((node.left, total+node.left.val, path+[node.left.val]))
+            if node.right: stack.append((node.right, total+node.right.val, path+[node.right.val]))
+                
+        return ans

problems/path-sum.py

@@ -11,4 +11,27 @@ def hasPathSum(self, root, S):
             if not node.left and not node.right and s==S: return True
             if node.left: stack.append((node.left, s))
             if node.right: stack.append((node.right, s))
-        return False
+        return False
+
+
+"""
+Time: O(N)
+Space: O(N)
+
+DFS
+"""
+class Solution(object):
+    def hasPathSum(self, root, targetSum):
+        if not root: return False
+        
+        stack = [(root, root.val)]
+        
+        while stack:
+            node, total = stack.pop()
+            
+            if not node.left and not node.right and total==targetSum: return True
+            if node.left: stack.append((node.left, total+node.left.val))
+            if node.right: stack.append((node.right, total+node.right.val))
+            
+        return False
+