思路

带边权并查集

#include <cstring>
#include <algorithm>
#include <iostream>
#include <map>
using namespace std;
unordered_map<int,int> S;
const int N=20010;
int p[N];
int d[N];//到根节点的距离
int n,m;
int find(int x){
    if(p[x]!=x){
        int root = find(p[x]);
        d[x] += d[p[x]];
        p[x] = root;
    }
    return p[x];
}
int get(int x){//离散化
    if(S.count(x)==0)S[x]=++n;
    return S[x];
}
int main(){
    cin >> n >> m;
    n=0;
    int res=m;
    for (int i = 0; i < N; i ++ ) p[i] = i;
    for(int i=1;i<=m;i++){
        int a,b;
        string t;
        cin >> a >> b >> t;
        a=get(a-1);b=get(b);//注意这里是a-1，因为查的是l-1和r的奇偶性
        int pa=find(a);int pb=find(b);
        int temp=0;
        if (t == "odd") temp = 1;
        if(pa==pb){
            if(((d[a] + d[b]) % 2 + 2) % 2 !=temp){
                res=i-1;
                break;
            }
        }else{
            p[pa]=pb;
            d[pa]=d[a]^d[b]^temp;
        }
    }
    cout << res;
}