树的子树

判断一棵树是否是另一棵树的子树

public class Solution {
    public boolean HasSubtree(TreeNode root1,TreeNode root2) {
        boolean result = false;
        if(root1 == null || root2 == null) return false;
        if(root1!=null && root2!=null){
            if(root1.val == root2.val){
                result = SameTree(root1,root2);
            }
            if(!result){
                result = HasSubtree(root1.left,root2);
            }
            if(!result){
                result = HasSubtree(root1.right,root2);
            }
        }
        return result;
    }
    public boolean SameTree(TreeNode root1,TreeNode root2){
        if(root1 == null && root2 == null){
            return true;
        }
        if(root1 == null &&root2!=null){
            return false;
        }
        if(root1!=null && root2 == null){ //子树就是两棵树都到头时才能返回真
            return false;
        }
        if(root1.val != root2.val){
            return false;
        }
        return SameTree(root1.left,root2.left)&&SameTree(root1.right,root2.right);
    }

}