UVa10158 War（并查集）

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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.csdn.net/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;}

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