UVA 1160 X-Plosives

题意是一次装入物品，物品由两种元素组成，当遇到即将装入的物品与已经装入的物品形成k个物品，k种元素，跳过该物品的装入。可以将每种元素看成顶点，物品看成一条边。这样问题就转化为利用并查集求环的情况。

算法竞赛训练指南中的代码：

#include <iostream>
#include <cstdio>
#include <climits>
#include <cstring>
#include <cstdlib>
#include <cmath>
#include <vector>
#include <queue>
#include <algorithm>
#define esp 1e-6
#define pb push_back
#define in  freopen("in.txt", "r", stdin);
#define out freopen("out.txt", "w", stdout);
#define print(a) printf("%d
",(a));
#define bug puts("********))))))");
#define Rep(i, c) for(__typeof(c.end()) i = c.begin(); i != c.end(); i++)
#define inf 0x0f0f0f0f
using namespace std;
typedef long long  LL;
typedef vector<int> VI;
typedef pair<int, int> pii;
typedef vector<pii,int> VII;
typedef vector<int>:: iterator IT;

#define N (int)(1e5+100)
int pa[N], rank[N];
void init(void)
{
    for(int i = 0; i < N; i++)
        pa[i] = i;
    memset(rank, 0, sizeof(rank));
}
void merge(int x, int y)
{
    if(rank[x] > rank[y])
        pa[y] = x;
    else {
        pa[x] = y;
        if(rank[x] == rank[y])
            rank[y]++;
    }
}
int findset(int x)
{
    return  (pa[x] == x) ? x: pa[x] = findset(pa[x]);
}
int main(void)
{
int x, y;
    while(~scanf("%d", &x))
    {
        int cnt = 0;
        init();
        while(x != -1)
        {
            scanf("%d", &y);
            x = findset(x), y = findset(y);
            if(x == y)
                cnt++;
                else merge(x, y);
            scanf("%d", &x);
        }
        printf("%d
", cnt);
    }
    return 0;
}