【种类并查集】 - poj2912

最新推荐文章于 2022-03-27 22:50:36 发布

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博客围绕poj2912展开，涉及种类并查集相关内容，但具体细节未详细给出，仅提及参考博客。

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参考：参考博客
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#include <iostream>
#include <algorithm>
using namespace std;
const int maxn = 50010;
int n, m;
struct node
{
    int x, y;
    int rel;
    node() {}
    node(int _x, int _y, int _rel) : x(_x), y(_y), rel(_rel) {}
} a[maxn];

int father[maxn];
int relation[maxn];
int change(char c)
{
    if (c == '=')
    {
        return 0;
    }
    else if (c == '<')
    {
        return 1;
    }
    else
    {
        return 2;
    }
}

void init()
{
    for (int i = 0; i <= n; i++)
    {
        father[i] = i;
        relation[i] = 0;
    }
}

int find(int x)
{
    if (father[x] == x)
    {
        return x;
    }
    else
    {
        int tf = father[x];
        father[x] = find(father[x]);
        relation[x] = (relation[x] + relation[tf]) % 3;
        return father[x];
    }
}

bool unite(int x, int y, int ope)
{
    int faX = find(x);
    int faY = find(y);
    if (faX != faY)
    {
        father[faY] = faX;
        relation[faY] = ((3 - relation[y]) % 3 + ope - 1 + relation[x]) % 3;
    }
    else
    {
        int rex = (3 - relation[x]) % 3;
        if ((rex + relation[y]) % 3 != ope)
        {
            return false;
        }
    }
    return true;
}

int main()
{
    while (scanf("%d%d", &n, &m) == 2)
    {
        init();
        int l, r;
        char oper;
        for (int i = 1; i <= m; i++)
        {
            cin >> l >> oper >> r;
            int ope = change(oper);
            a[i] = node(l, r, ope);
        }
        int maxLine = 0;            //产生矛盾的最大行数
        int person = -1;            //记录下裁判编号
        int ans = 0;                //判断有多少合法的裁判人选
        for (int i = 0; i < n; i++) //枚举裁判
        {
            bool flag = false; //是否会产生矛盾
            init();
            for (int j = 1; j <= m; j++)
            {
                if (a[j].x == i || a[j].y == i) ///排除带i的边
                {
                    continue;
                }
                if (!unite(a[j].x, a[j].y, a[j].rel))
                {
                    maxLine = max(maxLine, j);
                    flag = true;
                    break; //如果这里不跳出循环，就会改变maxLine的值，也就是这里发生错误的情况下，就不能继续向下搜索
                }
            }
            if (!flag)
            {
                ans++;
                person = i;
            }
        }
        if (ans == 1)
        {
            cout << "Player " << person << " can be determined to be the judge after " << maxLine << " lines" << endl;
        }
        else if (ans > 1)
        {
            cout << "Can not determine" << endl;
        }
        else
        {
            cout << "Impossible" << endl;
        }
    }
    return 0;
}