DMOPC '22 Contest 1 P3 - Group Project
View as PDFYou are the teacher of a class of  students, all but 
 pairs of which are friends. A friend group is a group of 
 or 
 people such that each person in the group is friends with at least 
 other people in the group. Your next class assignment requires the students to work in groups of 
. To "encourage new friendships and social interaction," you want to see if you can pick a group of 
 that does not contain a friend group. Of course, friendships in the class are constantly evolving. Thus, you would like to determine whether it is still possible to pick a group of 
 that does not contain a friend group after each of 
 changes.
Constraints
Subtask 1 [50%]
Subtask 2 [50%]
No additional constraints.
Input Specification
The first line contains  integers 
, 
, and 
.
The next  lines each contain 
 integers 
 and 
, indicating that students 
 and 
 are not friends. All pairs not mentioned here are originally friends.
The next  lines each contain 
 integers 
 and 
, indicating a change in the friendship status of students 
 and 
; they become friends if they weren't friends previously and vice versa.
Output Specification
Output  lines, the 
-th line containing the answer after the first 
 changes. The answer should be either 
YES if it is possible to pick a group of  that does not contain a friend group or 
NO otherwise.
Sample Input
6 3 1
1 2
1 3
2 4
1 2
Sample Output
YES
NO
Explanation for Sample
Initially, the graph looks like this (with edges denoting a friendship):
It can be shown that there is no friend group within the group of students . However, after the update:
All groups of  contain a friend group, so it is impossible to pick a group of 
 that does not contain a friend group.
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