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  • P3605【USACO 2015 Dec Platinum】Max Flow
    限制 : 时间限制 : 10000 MS   空间限制 : 65536 KB
    问题描述

    FJ给他的牛棚的N(2≤N≤50,000)个隔间之间安装了N-1根管道,隔间编号从1到N。所有隔间都被管道连通了。
    FJ有K(1≤K≤100,000)条运输牛奶的路线,第i条路线从隔间si运输到隔间ti。一条运输路线会给它的两个端点处的隔间以及中间途径的所有隔间带来一个单位的运输压力,你需要计算压力最大的隔间的压力是多少。

    Farmer John has installed a new system of N−1 pipes to transport milk between the N stalls in his barn (2≤N≤50,000), conveniently numbered 1,...,N. Each pipe connects a pair of stalls, and all stalls are connected to each-other via paths of pipes.
    FJ is pumping milk between K pairs of stalls (1≤K≤100,000). For the ith such pair, you are told two stalls si and ti, endpoints of a path along which milk is being pumped at a unit rate. FJ is concerned that some stalls might end up overwhelmed with all the milk being pumped through them, since a stall can serve as a waypoint along many of the K paths along which milk is being pumped. Please help him determine the maximum amount of milk being pumped through any stall. If milk is being pumped along a path from si to ti, then it counts as being pumped through the endpoint stalls si and ti, as well as through every stall along the path between them.

    输入格式

    The first line of the input contains N and K.
    The next N−1 lines each contain two integers x and y (x≠y) describing a pipe between stalls x and y.
    The next K lines each contain two integers s and t describing the endpoint stalls of a path through which milk is being pumped.

    第一行两个正整数N,K。
    接下来N-1行,每行两个整数x,y(x≠y),表示有一条管道连接牛棚隔间x和y。
    接下来K行,每行两个整数s,t,表示一条运输路线。

    输出格式

    An integer specifying the maximum amount of milk pumped through any stall in the barn.

    输出一个整数,表示运输压力最大的隔间的运输压力是多少。

    样例输入

    5 10
    3 4
    1 5
    4 2
    5 4
    5 4
    5 4
    3 5
    4 3
    4 3
    1 3
    3 5
    5 4
    1 5
    3 4

    样例输出

    9


    来源  感谢nodgd搬运并翻译