1022 Sum of Root To Leaf Binary Numbers.py

Author: rajeevranjancom

1022 Sum of Root To Leaf Binary Numbers.py

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+#!/usr/bin/python3
+"""
+Given a binary tree, each node has value 0 or 1.  Each root-to-leaf path
+represents a binary number starting with the most significant bit.  For example,
+if the path is 0 -> 1 -> 1 -> 0 -> 1, then this could represent 01101 in binary,
+which is 13.
+
+For all leaves in the tree, consider the numbers represented by the path from
+the root to that leaf.
+
+Return the sum of these numbers.
+
+Example 1:
+Input: [1,0,1,0,1,0,1]
+Output: 22
+Explanation: (100) + (101) + (110) + (111) = 4 + 5 + 6 + 7 = 22
+
+Note:
+The number of nodes in the tree is between 1 and 1000.
+node.val is 0 or 1.
+The answer will not exceed 2^31 - 1.
+"""
+
+
+# Definition for a binary tree node.
+class TreeNode:
+    def __init__(self, x):
+        self.val = x
+        self.left = None
+        self.right = None
+
+
+class Solution:
+    def __init__(self):
+        self.ret = 0
+        self.lst = []
+
+    def sumRootToLeaf(self, root: TreeNode) -> int:
+        """
+        Brute force, keep a lst, space O(log n)
+        Error-prone
+        """
+        self.dfs(root)
+        return self.ret
+
+    def dfs(self, node):
+        if not node:
+            return
+
+        self.lst.append(node.val)  # error prone
+        if not node.left and not node.right:
+            # leaf
+            cur = 0
+            for a in self.lst:
+                cur <<= 1
+                cur += a
+            self.ret += cur
+        else:
+            self.dfs(node.left)
+            self.dfs(node.right)
+        self.lst.pop()