D**u
发帖数: 204 | 1 弄了半天搞出个证明来, 自己看着都不觉得漂亮, 就将就着读吧.
To make it clear, I think you mean: If the group is 2n people,
then everyone know >=n people; if 2n+1 people, then everyone
know >=n+1 people (not include himself).
Using induction:
1) The problem is true for 3,4 (easy to discuss)
For 2, if 2 people know each other, we still think it to be
a circle.
2) Suppose the problem is true for people up to 2n.
3) Let's think about the case when group has 2n+1 people.
People are A_1, ...A_(2n+1). In the subgroup A_1,.. |
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