Codeforces 891C Envy

Envy

感觉这种最小生成树上的啥题都差不多的解法。。

#include<bits/stdc++.h>
#define LL long long
#define fi first
#define se second
#define mk make_pair
#define PLL pair<LL, LL>
#define PLI pair<LL, int>
#define PII pair<int, int>
#define SZ(x) ((int)x.size())
#define ull unsigned long long

using namespace std;

const int N = 5e5 + 7;
const int inf = 0x3f3f3f3f;
const LL INF = 0x3f3f3f3f3f3f3f3f;
const int mod = 1e9 + 7;
const double eps = 1e-8;
const double PI = acos(-1);

int n, m, q, a[N], b[N], w[N], va[N], vb[N], e[N];
vector<int> vc[N];

int fa[N];
int getRoot(int x) {
    return fa[x] == x ? x : fa[x] = getRoot(fa[x]);
}

bool cmp(const int& a, const int& b) {
    return w[a] < w[b];
}

int main() {
    scanf("%d%d", &n, &m);
    for(int i = 1; i <= n; i++) fa[i] = i;
    for(int i = 1; i <= m; i++) {
        scanf("%d%d%d", &a[i], &b[i], &w[i]);
        vc[w[i]].push_back(i);
    }
    for(int i = 1; i <= 500000; i++) {
        if(!SZ(vc[i])) continue;
        for(auto& x : vc[i]) {
            va[x] = getRoot(a[x]);
            vb[x] = getRoot(b[x]);
        }
        for(auto& x : vc[i]) {
            fa[getRoot(b[x])] = getRoot(a[x]);
        }
    }
    scanf("%d", &q);
    while(q--) {
        bool flag = true;
        int num; scanf("%d", &num);
        for(int i = 1; i <= num; i++) scanf("%d", &e[i]);
        for(int i = 1; i <= num; i++) {
            if(va[e[i]] == vb[e[i]]) {
                flag = false;
                break;
            }
        }
        if(!flag) {
            puts("NO");
            continue;
        }
        sort(e + 1, e + 1 + num, cmp);
        for(int L = 1, R = 1; L <= num && flag; L = R) {
            while(R <= num && w[e[R]] == w[e[L]]) R++;
            for(int i = L; i < R; i++) {
                int x = va[e[i]], y = vb[e[i]];
                fa[x] = x, fa[y] = y;
            }
            for(int i = L; i < R; i++) {
                int x = va[e[i]], y = vb[e[i]];
                int u = getRoot(x), v = getRoot(y);
                if(u == v) {
                    flag = false;
                    break;
                }
                fa[v] = u;
            }
        }
        if(flag) puts("YES");
        else puts("NO");
    }
    return 0;
}

/*
*/