18. Lowest Common Ancestor

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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.

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 2 is a descendant of itself.

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

Output: 2

Explanation: The LCA of nodes 2 and 1 is 2.

Time Complexity

O(n)

Space Complexity

O(h)