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非常nice的一道行列式的题目。 考虑如果没有路径不相交这个限制的话，那么这个题就是一个行列式：设 a[i][j] 为从编号第i小的源点到编号第j小的汇点的路径条数，那么矩阵a[][]的行列式就是的答案，因为行列式的定义就是给行一个列的排列，贡献就是所有a[i][p[i]]再乘上 (-1)^(p[] 阅读全文
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把lcm写成 (a+n)*(b+n) / gcd(a+n,b+n). 因为gcd可以辗转相减，所以就成了gcd(abs(a-b),a+n),一个常量一个变量之间的gcd,我们可以直接把abs(a-b)的所有约数找出来，然后看a要有某个约数的话n至少是多少，更新答案即可。(因为1e9以下的数的最多的约 阅读全文
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Discription Farmer John is hosting a tennis tournament with his n cows. Each cow has a skill level si, and no two cows having the same skill level. Ev 阅读全文
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Problem Statement There is an integer sequence A of length N. Find the number of the pairs of integers l and r (1≤l≤r≤N) that satisfy the following co 阅读全文
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Problem Statement There are N people standing in a row from west to east. Each person is facing east or west. The directions of the people is given as 阅读全文