problem_236.java

/*
236. 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).” */
class Solution {
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q) {
        if(root == null) return null;
        if(root == p || root == q) return root;
        TreeNode left = lowestCommonAncestor(root.left, p ,q);
        TreeNode right = lowestCommonAncestor(root.right, p ,q);
        if(left != null && right != null) return root;
        return (left != null)? left : right;
    }
}