求两个节点的最低公共祖先

package com.zhaochao.tree;

/**
 * Created by zhaochao on 17/1/24.
 * lowest common ancestor
 */
public class LCA {
    // 在root为根的二叉树中找A,B的LCA:
    // 如果找到了就返回这个LCA
    // 如果只碰到A，就返回A
    // 如果只碰到B，就返回B
    // 如果都没有，就返回null
    public TreeNode LCARec(TreeNode root, TreeNode rootA, TreeNode rootB) {

        if(root == null || root == rootA || root == rootB) {
            return root;
        }

        TreeNode left = LCARec(root.left, rootA, rootB);
        TreeNode right = LCARec(root.right, rootA,rootB);

        if(left != null && right != null) {
            return root;
        }

        if(left != null) {
            return left;
        }

        if(right != null) {
            return right;
        }

        return null;

    }
}