【简单并查集】 --poj2236

题目来源：poj 2236 Wireless Network

注意：

在合并时，我们只需要考虑这台电脑与之前已经修复的电脑能够通讯。设置一个vis数组。

#include <iostream>
using namespace std;
const int maxn = 1010;
int father[maxn]; //父亲数组
int height[maxn]; //树的高度

int N, d;
typedef pair<int, int> pii;
pii a[maxn];
bool vis[maxn];

//初始化N个元素
void init()
{
    for (int i = 1; i <= N; i++)
    {
        father[i] = i; //令father[i]=-1也可以
        vis[i] = false;
        height[i] = 0;
    }
}

//查找树的根
int find(int x)
{
    if (father[x] == x)
    {
        return x;
    }
    else
    {
        return find(father[x]);
    }
}

//合并x和y所属的集合
void unite(int x, int y)
{
    int faX = find(x);
    int faY = find(y);
    if (faX == faY)
    {
        return;
    }
    if (height[faX] < height[faY])
    {
        father[faX] = faY;
    }
    else
    {
        father[faY] = faX;
        if (height[faX] == height[faY])
        {
            height[faX]++;
        }
    }
}

//判断x和y是否属于同一个集合
bool same(int x, int y)
{
    return find(x) == find(y);
}

int dis(int i, int j)
{
    return (int)(a[i].first - a[j].first) * (a[i].first - a[j].first) + (a[i].second - a[j].second) * (a[i].second - a[j].second);
}

int main()
{
    while (scanf("%d%d", &N, &d) == 2)
    {
        init();
        int x, y;
        for (int i = 1; i <= N; i++)
        {
            cin >> x >> y;
            a[i] = make_pair(x, y);
        }
        char ope[3];
        while (~scanf("%s", ope))
        {
            if (ope[0] == 'O')
            {
                int id;
                cin >> id;
                vis[id] = true;
                for (int i = 1; i <= N; i++)
                {
                    if (vis[i] && dis(i, id) <= d * d)
                    {
                        unite(i, id);
                    }
                }
            }
            else if (ope[0] == 'S')
            {
                int x, y;
                cin >> x >> y;
                if (find(x) == find(y))
                {
                    cout << "SUCCESS" << endl;
                }
                else
                {
                    cout << "FAIL" << endl;
                }
            }
        }
    }
    return 0;
}