剑指Offer:面试题18——树的子结构(java实现)

问题描述：

输入两棵二叉树A和B，判断B是不是A的子结构。二叉树结点的定义如下：

public class TreeNode {
    int val = 0;
    TreeNode left = null;
    TreeNode right = null;

    public TreeNode(int val) {
        this.val = val;

    }

}

思路1：

递归

public static boolean HasSubtree(TreeNode root1,TreeNode root2) {
        boolean result = false;

        if(root1 != null && root2 != null){

            if(root1.val == root2.val){
                result = DoesTree1HaveTree2(root1, root2);
            }

            if(!result){
                result = HasSubtree(root1.left, root2);
            }

            if(!result){
                result = HasSubtree(root1.right, root2);
            }
        }

        return result;
    }

    public static boolean DoesTree1HaveTree2(TreeNode root1, TreeNode root2)
    {
        if(root2 == null){
            return true;
        }

        if(root1 == null){
            return false;
        }

        if(root1.val != root2.val){
            return false;
        }

        return DoesTree1HaveTree2(root1.left, root2.left) && DoesTree1HaveTree2(root1.right, root2.right);
    }