P2913 [USACO08OCT]车轮旋转Wheel Rotation

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  • 题目提供者 FarmerJohn2
  • 评测方式 云端评测
  • 标签 USACO 2008
  • 难度 普及-
  • 时空限制 1000ms / 128MB

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    题目描述

    Farmer John has an old-time thresher (wheat harvester) that requires belts to be installed on various gears to turn the parts. The engine drives pulley 1 in a clockwise direction which attaches via a belt to pulley 2. Pulley 2 attaches via a belt to pulley 3 and so on through a total of N (2 <= N <= 1,000) pulleys (and N-1 belts).

    The diagram above depicts the two ways a belt can be installed between two gears. In this illustration, pulley 1's belt directly drives pulley 2 (a 'straight' connection) and thus they will rotate in the same direction. Pulley 3 drives pulley 4 via a 'crossed belt' that reverses the direction of the rotation.

    Given a list of the belt types that connect the pulleys along with the fact that pulley 1 is driven in a clockwise direction by the engine, determine the drive direction of pulley N. Each belt is described by three integers:

    * S_i -- the driving (source) pulley 
    * D_i -- the driven (destination) pulley 
    * C_i -- the connection type (0=straight, 1=crossed) 
    Unfortunately, FJ lists the belts in random order. 
    By way of example, consider the illustration below. N = 4, and pulley 1 is driven clockwise by the thresher engine. Straight 
    belts drive pulley 2 and then pulley 3, so they rotate clockwise. The crosswise belt reverses the rotation direction so pulley 4 (pulley N) rotates counterclockwise. 

    POINTS: 70 约翰有一个过时的收割机,需要在它的各种滑轮上装配皮带才能让收割机的各个部分运作起 来.引擎能够驱动滑轮1向顺时针方向转动,滑轮1通过一条皮带又连接到滑轮2.滑轮2又通过一 条皮带连接到滑轮3,等等,总共有N(2 <= N <= 1000)个滑轮和N - 1条皮带.

    皮带连接两个滑轮有两种方式:直接连接和交叉连接.直接连接的两个滑轮旋转方向相同, 即同为顺时针或同为逆时针.交叉连接的两个滑轮旋转方向相反.

    现在给出一个列表,里面列出所有皮带的连接方式.已经知道滑轮1被引擎驱动着向顺时针方 向转动.每一条皮带由下面三个数定义:

    •驱动滑轮S,输入驱动力的滑轮.

    •被驱动滑轮D;,被驱使转动的滑轮.

    •连接类型C,0表示直接连接,1表示交叉连接.

    不幸的是,约翰的这个列表中,皮带的顺序是混乱的.所以请你写一个程序来求出滑轮N的 转动方向.

    输入输出格式

    输入格式:

    * Line 1: A single integer: N

    * Lines 2..N: Each line describes a belt with three integers: S_i, D_i, and C_i

    输出格式:

    * Line 1: A single integer that is the rotation direction for pulley N (0=clockwise, 1=counterclockwise)

    输入输出样例

    输入样例#1: 复制
    4 
    2 3 0 
    3 4 1 
    1 2 0 
    
    输出样例#1: 复制
    1 
    

    说明

    As in the example illustration.

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