1 #include <iostream>
2 #include <cstdlib>
3 #include <cstring>
4 #include <queue>
5 #include <cstdio>
6 #include <algorithm>
7 #include <map>
8 #define LL long long
9
10 using namespace std;
11
12 const int N = 2e5,M = 2e3;
13
14 struct DLX
15 {
16 int n,m,size;
17 int up[N],down[N],right[N],left[N],row[N],col[N]; //four pointer and the coordinate of nodes
18 int Head[M],Size[M]; //head pointer and the size of each linkList
19 int ans[M],ansd;
20 void init(int _n,int _m) //initialize the head line node
21 {
22 n = _n;
23 m = _m;
24 for(int i = 0; i <= m; i++)
25 {
26 Size[i] = 0;
27 up[i] = down[i] = i; //each column point to itself
28 left[i] = i-1; //row point to their neighbor
29 right[i] = i+1;
30 }
31 right[m] = 0;
32 left[0] = m; //circulate link
33 size = m;
34 for(int i = 1; i <= n; i++)
35 Head[i] = -1;
36 }
37 void Link(int r,int c) //modify the four pointer
38 {
39 ++Size[col[++size]=c];
40 row[size] = r;
41 down[size] = down[c];
42 up[down[c]] = size;
43 up[size] = c;
44 down[c] = size;
45
46 if(Head[r] < 0) Head[r] = left[size] = right[size] = size;
47 else
48 {
49 right[size] = right[Head[r]];
50 left[right[Head[r]]] = size;
51 left[size] = Head[r];
52 right[Head[r]] = size;
53 }
54 }
55
56 void remove(int c) //delete the column
57 {
58 left[right[c]] = left[c];
59 right[left[c]] = right[c];
60 for(int i = down[c]; i != c;i = down[i])
61 for(int j = right[i]; j != i; j = right[j])
62 {
63 up[down[j]] = up[j];
64 down[up[j]] = down[j];
65 --Size[col[j]];
66 }
67 }
68
69 void resume(int c)
70 {
71
72 for(int i = up[c]; i != c; i = up[i])
73 for(int j = left[i]; j != i; j = left[j])
74 {
75 ++Size[col[up[down[j]]=down[up[j]]=j]];
76 }
77 left[right[c]] = right[left[c]] = c;
78 }
79
80 bool dance(int d) //the depth
81 {
82 if(right[0] == 0)
83 {
84 ansd = d;
85 return true;
86 }
87
88 int c = right[0];
89 for(int i = right[0]; i != 0; i = right[i])
90 {
91 //if(Size[i] == 0) return false;
92 if(Size[i] < Size[c])
93 c = i;
94 }
95 remove(c);
96 for(int i = down[c]; i != c; i = down[i])
97 {
98 ans[d] = row[i];
99 for(int j = right[i]; j != i; j = right[j]) remove(col[j]);
100 if(dance(d+1)) return true;
101 for(int j = left[i]; j != i; j = left[j]) resume(col[j]);
102 }
103 resume(c);
104 return false;
105 }
106 };
107
108 DLX g;
109
110 void solve(int n,int m)
111 {
112 // int n,m;
113 // scanf("%d %d",&n,&m);
114
115
116 g.init(n,m);
117 for(int i = 1; i <= n; i++)
118 {
119 int t;
120 scanf("%d",&t);
121 for(int j = 1; j <= t; j++)
122 {
123 int num;
124 scanf("%d",&num);
125 g.Link(i,num);
126 }
127 }
128 if( !g.dance(0))
129 printf("NO
");
130 else
131 {
132 printf("%d ",g.ansd);
133 for(int i = 0; i < g.ansd; i++)
134 {
135 printf("%d%c",g.ans[i],i == g.ansd - 1?'
':' ');
136 }
137 }
138
139 }
140
141 int main(void)
142 {
143 int n,m;
144 while(scanf("%d %d",&n,&m) != -1)
145 {
146 solve(n,m);
147 }
148 return 0;
149 }
