LA 3644 X-Plosives (简单并查集) 判断是否存在环

X-Plosives

 

A secret service developed a new kind ofexplosive that attain its volatile property only when a specific association ofproducts occurs. Each product is a mix of two different simple compounds, towhich we call abinding pair. If N>2, thenmixing N different binding pairs containing N simple compounds creates apowerful explosive.For example, the bindingpairs A+B, B+C, A+C (three pairs, three compounds) result in an explosive,while A+B, B+C, A+D (three pairs, four compounds) does not.

 

You are not a secret agent but only a guyin a delivery agency with one dangerous problem: receive binding pairs insequential order and place them in a cargo ship. However, you must avoidplacing in the same room an explosive association. So, after placing a set ofpairs, if you receive one pair that might produce an explosion with some of thepairs already in stock, you must refuse it, otherwise, you must accept it.

 

An example. Let’s assume you receive thefollowing sequence: A+B, G+B, D+F, A+E, E+G, F+H. You would accept the firstfour pairs but then refuse E+G since it would be possible to make the followingexplosive with the previous pairs: A+B, G+B, A+E, E+G (4 pairs with 4 simplecompounds). Finally, you would accept the last pair, F+H.

 

Compute thenumber of refusals given a sequence of binding pairs.

 

Input

The input will contain several test cases, each of them as described below.Consecutive test cases are separated by a single blank line.
Instead of letters we will use integersto represent compounds. The input contains several lines. Each line(except the last) consists of two integers (each integer lies between 0 and 105)separated by a single space, representing a binding pair. The input ends in aline with the number –1. You may assume that no repeated binding pairsappears in the input.

 

Output

For each test case, a single line with the number ofrefusals.

 

Sample Input

1 2

3 4

3 5

3 1

2 3

4 1

2 6

6 5

-1

 

Sample Output

3

题意：   有一些简单化合物   每个化合物由2中不同元素组成        然后按照顺序依次将这些化合物放进车里   但是如果车上存在k个简单化合物 且正好包含k中元素的话

那么他们将变成易爆的化合物   为安全起见     每当你拿到一个化合物的时候   如果它和已装车的化合物形成易爆化合物   你就应当拒绝装车  否则就应该装车 。请输出有多少个化合物没有装车
分析： 把每个元素看做一个点，判断是否存在环，若加入的化合物可以构成环则不装车，否则装车。

代码：（未经评测，参考刘汝佳入门指南）

 

#include<cstdio>
using namespace std;
const int maxn=1e5+8;
int a[maxn];
int findset(int x)
{
    return a[x]==x? x:findset(a[x]);///路径压缩
}
int main()
{
    int x,y,ans=0;
    for(int i=0;i<=maxn;i++) a[i]=i;
    while(scanf("%d",&x)==1)
    {
        while(x!=-1)
        {
            scanf("%d",&y);
            int x1=findset(x);
            int y1=findset(y);
            if(x1==y1) ans++;
              else a[x1]=y1;
            scanf("%d",&x);
        }
        printf("%d\n",ans);
    }
    return 0;
}