Dynamic MST (Change weight of kth edge)

//Make CSP great again
//Vengeance
#include <bits/stdc++.h>
#define TASK "TESTCODE"
#define Log2(x) 31 - __builtin_clz(x)
using namespace std;
const int N = 2e4, M = 1e5;
int last[M + 1];
struct DSU
{
    int lab[N + 1];
    void reset(int n)
    {
        fill(lab + 1, lab + n + 1, -1);
    }
    int FindSet(int u)
    {
        return lab[u] < 0 ? u : lab[u] = FindSet(lab[u]);
    }
    bool unite(int u, int v)
    {
        u = FindSet(u);
        v = FindSet(v);
        if (u == v)
        {
            return false;
        }
        if (lab[u] > lab[v])
        {
            swap(u, v);
        }
        lab[u] += lab[v];
        lab[v] = u;
        return true;
    }
} dsu1, dsu2;
struct edge
{
    int l, r;
    int u, v, w;
    edge(int _l, int _r, int _u, int _v, int _w)
    {
        l = _l;
        r = _r;
        u = _u;
        v = _v;
        w = _w;
    }
    bool operator < (const edge & other) const
    {
        return w < other.w;
    }
};
int x[M + 1], y[M + 1], w[M + 1], id[M + 1];
int n, m, q;
vector<edge> all;
void read()
{
    cin >> n >> m >> q;
    for (int i = 1; i <= m; ++ i)
    {
        cin >> x[i] >> y[i] >> w[i];
    }
    for (int i = 1; i <= q; ++ i)
    {
        int k, d;
        cin >> k >> d;
        all.emplace_back(last[k], i - 1, x[k], y[k], w[k]);
        last[k] = i;
        w[k] = d;
    }
    for (int i = 1; i <= m; ++ i)
    {
        all.emplace_back(last[i], q, x[i], y[i], w[i]);
    }
    sort(all.begin(), all.end());
}
void DnC(int l, int r, int n, vector<edge> e, long long sum)
{
    e.erase(stable_partition(e.begin(), e.end(), [&](const edge &u) {return !(u.r < l || u.l > r);}), e.end());
    dsu1.reset(n);
    dsu2.reset(n);
    for (int i = 0; i < e.size(); ++ i)
    {
        if (e[i].r < r || e[i].l > l)
        {
            dsu1.unite(e[i].u, e[i].v);
        }
    }
    for (int i = 0; i < e.size(); ++ i)
    {
        if (e[i].l <= l && e[i].r >= r)
        {
            if (dsu1.unite(e[i].u, e[i].v))
            {
                sum += e[i].w;
                dsu2.unite(e[i].u, e[i].v);
            }
        }
    }
    if (l == r)
    {
        if (l > 0)
        {
            cout << sum << '\n';
        }
        return;
    }
    int sz = 0;
    for (int i = 1; i <= n; ++ i)
    {
        if (dsu2.lab[i] < 0)
        {
            id[i] = ++sz;
        }
    }
    dsu1.reset(n);
    for (int i = 0; i < e.size(); ++ i)
    {
        e[i].u = id[dsu2.FindSet(e[i].u)];
        e[i].v = id[dsu2.FindSet(e[i].v)];
        if (e[i].l <= l && e[i].r >= r && !dsu1.unite(e[i].u, e[i].v))
        {
            e[i].r = -1e9;
            e[i].l = 1e9;
        }
    }
    int mid = (l + r)/2;
    DnC(l, mid, sz, e, sum);
    DnC(mid + 1, r, sz, e, sum);
}
void solve()
{
    DnC(0, q, n, all, 0);
}
int main()
{
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr);
    if (fopen(TASK".INP", "r"))
    {
        freopen(TASK".INP", "r", stdin);
        //freopen(TASK".OUT", "w", stdout);
    }
    int t = 1;
    bool typetest = false;
    if (typetest)
    {
        cin >> t;
    }
    for (int __ = 1; __ <= t; ++ __)
    {
        //cout << "Case " << __ << ": ";
        read();
        solve();
    }
}