Fools and Foolproof Roads

并查集瞎搞搞就行， 有点小坑点。

#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 = 2e5 + 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, p, q, num, fa[N], U = -1, V = -1;
LL cost[N];
vector<PII> vc;

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

int main() {
    scanf("%d%d%d%d", &n, &m, &p, &q);
    for(int i = 1; i <= n; i++) fa[i] = i;
    for(int i = 1; i <= m; i++) {
        int u, v, w; scanf("%d%d%d", &u, &v, &w);
        U = u; V = v;
        int x = getRoot(u);
        int y = getRoot(v);
        if(x == y) {
            cost[x] += w;
        } else {
            fa[x] = y;
            cost[y] += cost[x] + w;
        }
    }
    priority_queue<PLI, vector<PLI>, greater<PLI> > que;
    for(int i = 1; i <= n; i++)
        if(getRoot(i) == i) que.push(mk(cost[i], i)), num++;
    int need = num - q;
    if(need < 0 || need > p) {
        puts("NO");
        return 0;
    }
    while(need--) {
        p--;
        int u = que.top().se; que.pop();
        int v = que.top().se; que.pop();
        int x = getRoot(u), y = getRoot(v);
        vc.push_back(mk(u, v));
        U = u, V = v;
        LL ret = min(1000000000ll, cost[x] + cost[y] + 1);
        cost[y] += cost[x] + ret;
        que.push(mk(cost[y], y));
    }
    if(p && U == -1) {
        puts("NO");
        return 0;
    }
    while(p--) {
        vc.push_back(mk(U, V));
    }
    puts("YES");
    for(auto& t : vc) printf("%d %d\n", t.fi, t.se);
    return 0;
}

/*
*/