{"trustable":false,"prependHtml":"\u003cscript\u003e window.katexOptions \u003d { disable: true }; \u003c/script\u003e\n\u003cscript type\u003d\"text/x-mathjax-config\"\u003e\n MathJax.Hub.Config({\n tex2jax: {\n inlineMath: [[\u0027$$$\u0027,\u0027$$$\u0027], [\u0027$\u0027,\u0027$\u0027]],\n displayMath: [[\u0027$$$$$$\u0027,\u0027$$$$$$\u0027], [\u0027$$\u0027,\u0027$$\u0027]]\n }\n });\n\u003c/script\u003e\n\u003cscript async src\u003d\"https://mathjax.codeforces.org/MathJax.js?config\u003dTeX-AMS-MML_HTMLorMML\" type\u003d\"text/javascript\"\u003e\u003c/script\u003e","sections":[{"title":"","value":{"format":"HTML","content":"一共有N个学生跟M门课程,一个学生可以任意选门课,问是否能够达成以下条件构成M个学生组成的学生会: \u003cp\u003e\n 1.会里的每个学生都代表一门不同的课程(一个学生只能代表一门课)\u003cp\u003e\n 2.每门课都有课代表\u003cp\u003e\n\u003c/div\u003e"}},{"title":"Input","value":{"format":"HTML","content":"第一行一个T代表T组数据\u003cp\u003e\n接下来输入M N(M\u003c100,N\u003c300)\u003cp\u003e\n然后M行:\u003cp\u003e\n\u003cp\u003e\n第i行代表第i门课程,每行开始一个数字k,表示选这门课的人数,接下来是k个选这门课程的学生的编号。\u003cp\u003e"}},{"title":"Output","value":{"format":"HTML","content":"若能满足上面两个要求这输出”YES”,否则为”NO”\u003cp\u003e"}},{"title":"Sample Input","value":{"format":"HTML","content":"\u003cpre\u003e2\n3 3\n3 1 2 3\n2 1 2\n1 1\n3 3\n2 1 3\n2 1 3\n1 1\u003c/pre\u003e"}},{"title":"Sample Output","value":{"format":"HTML","content":"\u003cpre\u003eYES\nNO \u003c/pre\u003e"}},{"title":"","value":{"format":"HTML","content":""}}]}