day 30

Author: sachuverma

Leetcode Daily Challenge/June-2021/30. Lowest Common Ancestor of a Binary Tree.cpp

@@ -0,0 +1,55 @@
+/*
+Lowest Common Ancestor of a Binary Tree
+=======================================
+
+Given a binary tree, find the lowest common ancestor (LCA) of two given nodes in the tree.
+
+According to the definition of LCA on Wikipedia: “The lowest common ancestor is defined between two nodes p and q as the lowest node in T that has both p and q as descendants (where we allow a node to be a descendant of itself).”
+
+Example 1:
+Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 1
+Output: 3
+Explanation: The LCA of nodes 5 and 1 is 3.
+
+Example 2:
+Input: root = [3,5,1,6,2,0,8,null,null,7,4], p = 5, q = 4
+Output: 5
+Explanation: The LCA of nodes 5 and 4 is 5, since a node can be a descendant of itself according to the LCA definition.
+
+Example 3:
+Input: root = [1,2], p = 1, q = 2
+Output: 1
+
+Constraints:
+The number of nodes in the tree is in the range [2, 105].
+-109 <= Node.val <= 109
+All Node.val are unique.
+p != q
+p and q will exist in the tree.
+*/
+
+/**
+ * Definition for a binary tree node.
+ * struct TreeNode {
+ *     int val;
+ *     TreeNode *left;
+ *     TreeNode *right;
+ *     TreeNode(int x) : val(x), left(NULL), right(NULL) {}
+ * };
+ */
+
+class Solution
+{
+public:
+  TreeNode *lowestCommonAncestor(TreeNode *root, TreeNode *p, TreeNode *q)
+  {
+    if (!root || root == p || root == q)
+      return root;
+    auto left = lowestCommonAncestor(root->left, p, q);
+    auto right = lowestCommonAncestor(root->right, p, q);
+
+    if (left && right)
+      return root;
+    return left ? left : right;
+  }
+};

Leetcode Daily Challenge/June-2021/README.md

@@ -31,3 +31,4 @@
 | 27. | [Candy](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3793/) [cpp](./27.%20Candy.cpp)                                                                                                                      |
 | 28. | [Remove All Adjacent Duplicates In String](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/606/week-4-june-22nd-june-28th/3794/) [cpp](./28.%20Remove%20All%20Adjacent%20Duplicates%20In%20String.cpp)                                      |
 | 29. | [Max Consecutive Ones III](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/607/week-5-june-29th-june-30th/3796/) [cpp](./29.%20Max%20Consecutive%20Ones%20III.cpp)                                                                          |
+| 30. | [Lowest Common Ancestor of a Binary Tree](https://leetcode.com/explore/challenge/card/june-leetcoding-challenge-2021/607/week-5-june-29th-june-30th/3797/) [cpp](./30.%20Lowest%20Common%20Ancestor%20of%20a%20Binary%20Tree.cpp)                                                                          |