$ Loj526 \ [LibreOJ \ \ beta \ Round \ \ # 4] $ subset of graph theory

Correct answer: 图论

Report problem solving:

Portal $ QwQ $

Found not seek the largest group, then consider seeking maximum independent set also put all $ gcd (i, j) \ side connected between (i + 1, j + 1) dot cdot gcd = 1 $, and then seeking the most independent set.

Found still can not do, you might guess Conclusion: This map must be Zhang bipartite graph.

In fact, guessed proved quite $ easy $ of $ QwQ $

Found even parity between the edge points must be different, because, if the same, must be a multiple of $ $ GCD 2

So this is Zhang bipartite graph

Then finish spicy, $ over $