Runtime: 36 ms (Top 83.6%) | Memory: 16.39 MB (Top 54.5%)

Author: AnasImloul

scripts/algorithms/B/Binary Search Tree to Greater Sum Tree/Binary Search Tree to Greater Sum Tree.py

@@ -1,40 +1,13 @@
-# Runtime: 69 ms (Top 6.93%) | Memory: 14.1 MB (Top 33.83%)
-class Solution:
-    def bstToGst(self, root: TreeNode) -> TreeNode:
-        '''
-        Left - root - right : gives sorted ordering of nodes - O(n)
-        Then find prefix sum of the sorted array from the right side - O(n)
-        Then do binary search on inorder array and get the prefix sum - O(nlogn) since we do binary search for each node
-        '''
-
-        #find the inorder traversal
-        def inorder(node,arr):
-            if not node: return
-
-            inorder(node.left,arr)
-            arr.append(node.val)
-            inorder(node.right,arr)
-
-        arr = []
-        inorder(root,arr)
-        n = len(arr)
-
-        #find the prefix sum
-        prefix = [num for num in arr]
-        i = n-2
-        while i>=0:
-            prefix[i] += prefix[i+1]
-            i-=1
+# Runtime: 36 ms (Top 83.6%) | Memory: 16.39 MB (Top 54.5%)
 
-        #do binary search and fill in the prefix sum for each node
-        def fill(node):
-            if not node: return
-
-            i = bisect_left(arr,node.val)
-            node.val = prefix[i]
-
-            fill(node.right)
-            fill(node.left)
-
-        fill(root)
+class Solution:
+    def bstToGst(self, root):
+        self.total = 0
+        def dfs(n):
+            if n:
+                dfs(n.right)
+                self.total +=  n.val
+                n.val       =  self.total
+                dfs(n.left)
+        dfs(root)
         return root