2022-08-12 Daily-Challenge

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In: DailyChallenge

Today I have done leetcode's August LeetCoding Challenge with cpp.

August LeetCoding Challenge 12

Description

Lowest Common Ancestor of a Binary Search Tree

Given a binary search tree (BST), find the lowest common ancestor (LCA) node of two given nodes in the BST.

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:

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Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 8
Output: 6
Explanation: The LCA of nodes 2 and 8 is 6.

Example 2:

img

Input: root = [6,2,8,0,4,7,9,null,null,3,5], p = 2, q = 4
Output: 2
Explanation: The LCA of nodes 2 and 4 is 2, since a node can be a descendant of itself according to the LCA definition.

Example 3:

Input: root = [2,1], p = 2, q = 1
Output: 2

Constraints:

  • The number of nodes in the tree is in the range [2, 10^5].
  • -10^9 <= Node.val <= 10^9
  • All Node.val are unique.
  • p != q
  • p and q will exist in the BST.

Solution

class Solution {
public:
  TreeNode* lowestCommonAncestor(TreeNode* root, TreeNode* p, TreeNode* q) {
    if(!root || root == p || root == q) return root;
    TreeNode *left = lowestCommonAncestor(root->left, p, q);
    TreeNode *right = lowestCommonAncestor(root->right, p, q);
    if(left && right) return root;
    if(left) return left;
    if(right) return right;
    return nullptr;
  }
};

// Accepted
// 28/28 cases passed (40 ms)
// Your runtime beats 69.28 % of cpp submissions
// Your memory usage beats 91.99 % of cpp submissions (23.2 MB)
Algorithm