1017  Exact cover
Time Limit : 15 Second
Memory Limit : 128 MB
Special Judge
Submission: 7689
Solved: 3898
 Description
 There is an N*M matrix with only 0s and 1s, (1 <= N,M <= 1000). An exact cover is a selection of rows such that every column has a 1 in exactly one of the selected rows.
Try to find out the selected rows.
 Input
 There are multiply test cases.
First line: two integers N, M;
The following N lines: Every line first comes an integer C(1 <= C <= 100), represents the number of 1s in this row, then comes C integers: the index of the columns whose value is 1 in this row.
 Output
 First output the number of rows in the selection, then output the index of the selected rows.
If there are multiply selections, you should just output any of them.
If there are no selection, just output "NO".
 sample input

6 7 3 1 4 7 2 1 4 3 4 5 7 3 3 5 6 4 2 3 6 7 2 2 7
 sample output

3 2 4 6
 hint
 source
 dupeng