poj1733 Parity game

参见算法竞赛进阶指南190页

#include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;
int n, m, num[10005], qwq=1, fa[10005], dis[10005];
char ss[15];
struct Node{
	int l, r, ans;
}nd[5005];
int myfind(int x){
	if(x==fa[x])	return x;
	int rot=myfind(fa[x]);
	dis[x] ^= dis[fa[x]];
	return fa[x]=rot;
}
int main(){
	cin>>n>>m;
	n = 0;
	for(int i=1; i<=m; i++){
		scanf("%d %d %s", &nd[i].l, &nd[i].r, ss);
		nd[i].l--;
		nd[i].ans = ss[0]=='o';
		num[++n] = nd[i].l;
		num[++n] = nd[i].r;
	}
	sort(num+1, num+1+n);
	n = unique(num+1, num+1+n) - num - 1;
	for(int i=1; i<=m; i++){
		nd[i].l = lower_bound(num+1, num+1+n, nd[i].l) - num;
		nd[i].r = lower_bound(num+1, num+1+n, nd[i].r) - num;
	}
	for(int i=1; i<=n; i++)	fa[i] = i;
	for(int i=1; i<=m; i++){
		int r1=myfind(nd[i].l), r2=myfind(nd[i].r);
		if(r1==r2){
			if(nd[i].ans!=(dis[nd[i].l]^dis[nd[i].r]))	break;
		}
		else{
			fa[r1] = r2;
			dis[r1] = dis[nd[i].l] ^ dis[nd[i].r] ^ nd[i].ans;
		}
		qwq++;
	}
	printf("%d
", qwq-1);
	return 0;
}

另一种写法

#include <algorithm>
#include <iostream>
#include <cstdio>
using namespace std;
int n, m, num[10005], fa[20005];
char ss[15];
struct Node{
	int l, r, ans;
}nd[5005];
int p(int x){
	return x;
}
int q(int x){
	return x+n;
}
int myfind(int x){
	return fa[x]==x?x:fa[x]=myfind(fa[x]);
}
int main(){
	cin>>n>>m;
	n = 0;
	for(int i=1; i<=m; i++){
		scanf("%d %d %s", &nd[i].l, &nd[i].r, ss);
		nd[i].l--;
		nd[i].ans = ss[0]=='o';
		num[++n] = nd[i].l;
		num[++n] = nd[i].r;
	}
	sort(num+1, num+1+n);
	n = unique(num+1, num+1+n) - num - 1;
	for(int i=1; i<=m; i++){
		nd[i].l = lower_bound(num+1, num+1+n, nd[i].l) - num;
		nd[i].r = lower_bound(num+1, num+1+n, nd[i].r) - num;
	}
	for(int i=1; i<=n+n; i++)	fa[i] = i;
	for(int i=1; i<=m; i++){
		int uu=nd[i].l, vv=nd[i].r;
		if(myfind(p(uu))==myfind(q(vv)) || myfind(p(uu))==myfind(p(vv))){
			if(nd[i].ans!=(myfind(p(uu))==myfind(q(vv)))){
				cout<<i-1<<endl;
				return 0;
			}
		}
		else{
			if(nd[i].ans){
				fa[myfind(p(uu))] = myfind(q(vv));
				fa[myfind(q(uu))] = myfind(p(vv));
			}
			else{
				fa[myfind(p(uu))] = myfind(p(vv));
				fa[myfind(q(uu))] = myfind(q(vv));
			}
		}
	}
	cout<<m;
	return 0;
}