88题 Lowest Common Ancestor of a Binary Tree

Lowest Common Ancestor of a Binary Tree

Description
Given the root and two nodes in a Binary Tree. Find the lowest common ancestor(LCA) of the two nodes.

The lowest common ancestor is the node with largest depth which is the ancestor of both nodes.

/**
 * Definition of TreeNode:
 * public class TreeNode {
 *     public int val;
 *     public TreeNode left, right;
 *     public TreeNode(int val) {
 *         this.val = val;
 *         this.left = this.right = null;
 *     }
 * }
 */


public class Solution {
    /*
     * @param root: The root of the binary search tree.
     * @param A: A TreeNode in a Binary.
     * @param B: A TreeNode in a Binary.
     * @return: Return the least common ancestor(LCA) of the two nodes.
     */
    public TreeNode lowestCommonAncestor(TreeNode root, TreeNode A, TreeNode B) {
        // write your code here
        if(root == null || A == root || B == root){
             return root ;
        }
        TreeNode left = lowestCommonAncestor(root.left , A, B);
        TreeNode right = lowestCommonAncestor(root.right , A, B);
        if(left != null && right != null){
            return root ;
        }
        if(left != null){
            return left ;
        }
        if(right != null){
            return right ;
        }
        return null ;
    }
}