298. Binary Tree Longest Consecutive Sequence

Author: Partho Biswas

README.md

@@ -338,6 +338,7 @@ Check this [golden](https://tinyurl.com/ujopecz) post.
 |24| **[1110. Delete Nodes And Return Forest](https://tinyurl.com/rg8qomj)** | [Python](https://tinyurl.com/wu6rdaw/1110_Delete_Nodes_And_Return_Forest.py)| [Vid 1](https://tinyurl.com/t9rax3x), [Vid 2](https://tinyurl.com/uw6y3zk), [Art 1](https://tinyurl.com/ujopecz), [Art 2](https://tinyurl.com/tppglsu) | Medium | 📌 **TODO: Check again. Important |
 |25| [257. Binary Tree Paths](https://leetcode.com/problems/binary-tree-paths/)| [Python](https://tinyurl.com/wu6rdaw/257_Binary_Tree_Paths.py)| --- | Easy | DFS |
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+|27| **[298. Binary Tree Longest Consecutive Sequence](https://tinyurl.com/rw2sqxr)**| [Python](https://tinyurl.com/wu6rdaw/298_Binary_Tree_Longest_Consecutive_Sequence.py)| **[Art 1](https://tinyurl.com/wmlq6md)** | Medium | DFS |
 
 </p>
 </details>

leetcode.com/python/298_Binary_Tree_Longest_Consecutive_Sequence.py

@@ -0,0 +1,63 @@
+# Definition for a binary tree node.
+# class TreeNode(object):
+#     def __init__(self, x):
+#         self.val = x
+#         self.left = None
+#         self.right = None
+
+# Top-Down approach - Accepted
+class Solution(object):
+    def longestConsecutive(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        # if not root:
+        #     return 0
+        longestSeque = 0
+        longestSeque = self.longestConsecutiveHelper(root, None, 0, longestSeque)
+        return longestSeque
+
+    def longestConsecutiveHelper(self, root, parent, currentLongestSeque, longestSeque):
+        if not root:
+            return max(currentLongestSeque, longestSeque)
+        if parent and root.val == parent.val + 1:
+            currentLongestSeque += 1
+        else:
+            currentLongestSeque = 1
+        longestSeque = max(currentLongestSeque, longestSeque)
+        leftLength = self.longestConsecutiveHelper(root.left, root, currentLongestSeque, longestSeque)
+        rightLength = self.longestConsecutiveHelper(root.right, root, currentLongestSeque, longestSeque)
+        maxLength = max(leftLength, rightLength, longestSeque)
+        return maxLength
+
+
+
+
+# Bottom-Up approach - Accepted
+class Solution(object):
+    def longestConsecutive(self, root):
+        """
+        :type root: TreeNode
+        :rtype: int
+        """
+        if not root:
+            return 0
+        dummyNode = TreeNode(float("inf"))
+        dummyNode.left = root
+        longestSeque, val = self.longestConsecutiveHelper(dummyNode)
+        return longestSeque
+
+    def longestConsecutiveHelper(self, root):
+        if not root:
+            return (0, float("-inf"))
+        leftLength, leftVal = self.longestConsecutiveHelper(root.left)
+        rightLength, rightVal = self.longestConsecutiveHelper(root.right)
+
+        if leftVal != float("-inf") and root.val == leftVal - 1:
+            leftLength += 1
+        elif rightVal != float("-inf") and root.val == rightVal - 1:
+            rightLength += 1
+        longestSeque = max(leftLength, rightLength, 1)
+
+        return (longestSeque, root.val)