Parity game

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
#include<set>
using namespace std;
const int N=20010;
int
n,m,t,d[N],fa[N],a[N],l[N],r[N],ans[N];
void discrete()
{
	sort(a+1,a+t+1);
	n=unique(a+1,a+t+1)-a-1;
}
int get(int x)
{
	if(fa[x]==x) return x;
	int root=get(fa[x]); d[x]^=d[fa[x]];
	return fa[x]=root;
}
int main()
{
	scanf("%d%d",&n,&m);
	for(int i=1;i<=m;i++){
		scanf("%d%d",&l[i],&r[i]);
		char ch[5]; scanf("%s",ch);
		if(ch[0]=='o') ans[i]=1;
		else ans[i]=0;
		a[++t]=l[i]-1;
		a[++t]=r[i];
	}
	discrete();
	for(int i=1;i<=n;i++) fa[i]=i;
	for(int i=1;i<=m;i++){
		int x=lower_bound(a+1,a+n+1,l[i]-1)-a;
		int y=lower_bound(a+1,a+n+1,r[i])-a;
		int p=get(x),q=get(y);
		if(p==q){
			if((d[x]^d[y])!=ans[i]){
				cout<<i-1<<endl;
				return 0;
			}
		}
		else
			fa[p]=q,d[p]=d[x]^d[y]^ans[i];
	}
	cout<<m<<endl;
	return 0;
}