Accepted Java Solution


  • 5
    C
    /**
     * Definition for a binary tree node.
     * public class TreeNode {
     *     int val;
     *     TreeNode left;
     *     TreeNode right;
     *     TreeNode(int x) { val = x; }
     * }
     */
    public class Solution
    {
        public TreeNode lowestCommonAncestor(TreeNode root, TreeNode p, TreeNode q)
        {
            if(root == null)
                return null;
            if(root == p || root == q)
                return root; // if find at root, no need to continue, this is before branching
            TreeNode left = lowestCommonAncestor(root.left,p,q);
            TreeNode right = lowestCommonAncestor(root.right,p,q);
            if(left != null && right != null) //after branching
                return root;
            return left == null?right:left;//one branch null or branch not null, the brach without null automatically becomes the lca
                                            //both null and root doesn't match, then return null
        }
    }

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