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=====A=====
* 题意:一个序列为$0,1…n-1$,定义一个变换,每个位置$i$变换到位置$(i+a_i)\%n$处,$|a_i|\le10^9$,问是否有两个位置经过一次变换后变换到同一个位置
* 题解:注意$a_i$可为负数
=====B=====
* 题意:如果$N$和$S$在同一列或者同一行，那么$N$将会向$S$的方向移动一个单元格。现在给定一张图$n,m\le1000$，保证白格一定不会有$N$经过，黑格一定可以通过吸引使得$N$经过。又要求每行每列都必须至少有一个$S$。求最少安排多少个$N$可以达成要求。
* 题解:若能完成，答案必为黑格的连通块数。若不能完成,有以下几种情况
* 两个黑格之间有白格
* 有全为白格的行，无全为白格的列
* 有全为白格的列，无全为白格的行
=====C=====
* 题意:给出$n(n\le2*10^5)$个变元和一个由$m(m\le2*10^5)$个不等式组成的式子，每个不等式为$x_i