UVa10158 War（并查集）

最新推荐文章于 2018-05-07 23:46:19 发布

原创最新推荐文章于 2018-05-07 23:46:19 发布 · 552 阅读

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本文针对UVa10158War问题，通过并查集解决朋友与敌人的关系判断。文章包含作者自己的实现代码及遇到的问题，并分享了一段来自网络的参考代码。

题目链接：UVa10158 War（并查集）

这道题看着不难，也很明显是用并查集做，但是我自己写的代码一直是Runtime error，现在还是不知道为什么。网上找了一个题解，看了好长时间也没看懂。两份代码先都放这里吧，以后回头再看没准会懂。希望这样。

我自己写的代码：

#include <iostream>
#include <vector>
#include <algorithm>

using namespace std;

const int MAX_N = 10000 + 1000;
vector <int> enemies[MAX_N];
int p[MAX_N];
int u,v,x,y,c,N;

int setEnemies(int x,int y);
int setFriends(int x,int y);
bool areFriends(int x,int y);
bool areEnemies(int x,int y);
int Find(int x);
void Union(int u,int v);

int Find(int x)
{
    return p[x] == x ? x : (p[x] = Find(p[x]));
}
void Union(int u,int v)
{
    p[u] = v;
}
bool areFriends(int x,int y)
{
    u = Find(x);
    v = Find(y);
    if(u == v)
        return true;//已经是朋友
    return false;
}
bool areEnemies(int x,int y)
{
    vector<int>::iterator result = find(enemies[x].begin(),enemies[x].end(),y);
    if(result != enemies[x].end())
        return true;
    return false;
}
int setFriends(int x,int y)
{
    if(areEnemies(x,y))
        return -1;
    if(areFriends(x,y))
        return 1;
    u = Find(x);
    v = Find(y);
    if(u != v)
        Union(u,v);
    vector<int>:: iterator i;
    for(i = enemies[x].begin();i != enemies[x].end();i++)
    {
        if(!areEnemies(y,*i))
            setEnemies(y,*i);
    }
    for(i = enemies[y].begin();i != enemies[y].end();i++)
    {
        if(!areEnemies(x,*i))
            setEnemies(x,*i);
    }
    return 1;
}
int setEnemies(int x,int y)
{
    if(areFriends(x,y))
        return -1;
    if(areEnemies(y,x))
        return 1;
    vector<int>:: iterator i;
    for(i = enemies[x].begin();i != enemies[x].end();i++)
        setFriends(y,*i);
    for(i = enemies[y].begin();i != enemies[y].end();i++)
        setFriends(x,*i);
    int j;
    int x_f = Find(x);// x的朋友圈代表
    int y_f = Find(y);// y的朋友圈代表
    for(j = 0;j < N;j++)
    {
        if(x_f == Find(j) && j != x)
        {
            if(!areEnemies(j,y))
            {
                enemies[j].push_back(y);
                enemies[y].push_back(j);
            }
        }
        if(y_f == Find(j) && j != y)
        {
            if(!areEnemies(j,x))
            {
                enemies[j].push_back(x);
                enemies[x].push_back(j);
            }
        }
    }
    enemies[x].push_back(y);
    enemies[y].push_back(x);
}
int main()
{
    cin>>N;
    int i;
    for(i = 0;i < N;i++)
        p[i] = i;//编号从零开始
    while(cin>>c>>x>>y ,c || x || y)
    {
        switch(c)
        {
        case 1:
            if(setFriends(x,y) == -1)
                cout<<-1<<endl;
            break;
        case 2:
            if(setEnemies(x,y) == -1)
                cout<<-1<<endl;
            break;
        case 3:
            if(areFriends(x,y))
                cout<<1<<endl;
            else
                cout<<0<<endl;
            break;
        case 4:
            if(areEnemies(x,y))
                cout<<1<<endl;
            else
                cout<<0<<endl;
            break;
        }
    }
    return 0;
}

网上的代码：http://blog.youkuaiyun.com/ac_lion/article/details/8569846

#include <cstdio>
#include <cstring>

const int N = 20020;
int fa[N], n;
int find ( int a ) {
    return fa[a] == a ? a : fa[a] = find(fa[a]);
}
void setFriend( int a, int b ) {
    int x1, x2, y1, y2;
    x1 = find(a), y1 = find(b);
    x2 = find(a+n), y2 = find(b+n);
    if ( x1 == y2 || x2 == y1 ) printf("-1\n");
    else {
        fa[x1] = y1;
        fa[x2] = y2;
    }
}
void setEnemy( int a, int b ) {
    int x1, x2, y1, y2;
    x1 = find(a), y1 = find(b);
    x2 = find(a+n), y2 = find(b+n);
    if ( x1 == y1 ) printf("-1\n");
    else {
        fa[x1] = y2;
        fa[y1] = x2;
    }
}
void areFriend( int a, int b ) {
    int x, y;
    x = find(a);
    y = find(b);
    if ( x == y ) printf("1\n");
    else printf("0\n");
}
void areEnemy( int a, int b ) {
    int x1, x2, y1, y2;
    x1 = find(a), y1 = find(b);
    x2 = find(a+n), y2 = find(b+n);
    if ( x2 == y1 || x1 == y2 ) printf("1\n");
    else printf("0\n");
}

int main()
{
    while ( scanf("%d", &n) != EOF ) {
        int c, a, b;
        for ( int i = 0; i <= n*2; ++i ) fa[i] = i;
        while ( 1 ) {
            scanf("%d%d%d", &c, &a, &b);
            if ( a == 0 && c == 0 && b == 0 ) break;
            if ( c == 1 ) setFriend( a, b );
            else if ( c == 2 ) setEnemy( a, b );
            else if ( c == 3 ) areFriend( a, b );
            else if ( c == 4 ) areEnemy( a, b );
        }
    }
    return 0;
}