洛谷 P2913 [USACO08OCT]车轮旋转Wheel Rotation
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
说明
As in the example illustration.
思路:搜索。
#include<cstdio>
#include<cstring>
#include<iostream>
#include<algorithm>
#define MAXN 1010
using namespace std;
int n,tot;
int vis[MAXN];
int to[MAXN],head[MAXN],net[MAXN],cap[MAXN];
void add(int u,int v,int w){
to[++tot]=v;cap[tot]=w;net[tot]=head[u];head[u]=tot;
}
void dfs(int now,int fa){
for(int i=head[now];i;i=net[i])
if(to[i]!=fa){
if(cap[i]==) vis[to[i]]=vis[now];
else vis[to[i]]=!vis[now];
dfs(to[i],now);
}
}
int main(){
scanf("%d",&n);
for(int i=;i<n;i++){
int x,y,z;
scanf("%d%d%d",&x,&y,&z);
add(x,y,z);
}
vis[]=;
dfs(,);
cout<<vis[n];
}
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