标签归档:乘法逆元

Codeforces Round#369 Div.2

A. Bus to Udayland

ZS the Coder and Chris the Baboon are travelling to Udayland! To get there, they have to get on the special IOI bus. The IOI bus has nrows of seats. There are 4 seats in each row, and the seats are separated into pairs by a walkway. When ZS and Chris came, some places in the bus was already occupied.

ZS and Chris are good friends. They insist to get a pair of neighbouring empty seats. Two seats are considered neighbouring if they are in the same row and in the same pair. Given the configuration of the bus, can you help ZS and Chris determine where they should sit?

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[bzoj 1856][SCOI2010] 字符串

Description

lxhgww最近接到了一个生成字符串的任务,任务需要他把n个1和m个0组成字符串,但是任务还要求在组成的字符串中,在任意的前k个字符中,1的个数不能少于0的个数。现在lxhgww想要知道满足要求的字符串共有多少个,聪明的程序员们,你们能帮助他吗?

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