1650. Lowest Common Ancestor of a Binary Tree III

O(h) time O(1) space
跟160. Intersection of Two Linked Lists一样

/*
// Definition for a Node.
class Node {
public:
    int val;
    Node* left;
    Node* right;
    Node* parent;
};
*/

class Solution {
public:
    Node* lowestCommonAncestor(Node* p, Node * q) {
        auto a = p, b = q;
        while (a != b) {
            a = a ? a->parent : q;
            b = b ? b->parent : p;
        }
        return a;
    }
};