剑指Offer26.树的子结构

题目：https://leetcode-cn.com/problems/shu-de-zi-jie-gou-lcof/

代码：

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSubStructure(TreeNode A, TreeNode B) {
        if (A == null || B == null){
            return false;
        }
        if(A.val == B.val){
            if(check(A, B)){
                return true;
            }
        }
        return isSubStructure(A.left, B) || isSubStructure(A.right, B);
    }
    private boolean check(TreeNode a, TreeNode b){
        if(a == null && b != null){
            return false;
        }
        if(b == null){
            return true;
        }
        if(a.val != b.val){
            return false;
        }
        return check(a.left, b.left) && check(a.right, b.right);
    }
}