H.cpp

#include <bits/stdc++.h>
#define FOR(i,a,b) for(int i=(a),_b=(b); i<=_b; ++i)
#define FORD(i,a,b) for(int i=(a),_b=(b); i>=_b; --i)
#define REP(i,a) for(int i=0,_a=(a); i < _a; ++i)

#define DEBUG(X) { cout << #X << " = " << X << endl; }
#define PR(A,n)  { cout << #A << " = "; FOR(_,1,n) cout << A[_] << ' '; cout << endl; }
#define PR0(A,n) { cout << #A << " = "; REP(_,n) cout << A[_] << ' '; cout << endl; }

#define sqr(x) ((x) * (x))
#define ll long long
#define SZ(x) ((int) (x).size())
using namespace std;

template<class Flow=int, class Cost=ll>
struct MinCostFlow {
    const Flow INF_FLOW = 1000111000;
    const Cost INF_COST = 1000111000111000LL;

    int n, t, S, T;
    Flow totalFlow;
    Cost totalCost;
    vector<int> last, visited;
    vector<Cost> dis;
    struct Edge {
        int to;
        Flow cap;
        Cost cost;
        int next;
        Edge(int to, Flow cap, Cost cost, int next) :
                to(to), cap(cap), cost(cost), next(next) {}
    };
    vector<Edge> edges;

    MinCostFlow(int n) : n(n), t(0), totalFlow(0), totalCost(0), last(n, -1), visited(n, 0), dis(n, 0) {
        edges.clear();
    }

    int addEdge(int from, int to, Flow cap, Cost cost) {
        edges.push_back(Edge(to, cap, cost, last[from]));
        last[from] = t++;
        edges.push_back(Edge(from, 0, -cost, last[to]));
        last[to] = t++;
        return t - 2;
    }

    pair<Flow, Cost> minCostFlow(int _S, int _T) {
        S = _S; T = _T;
        SPFA();
        while (1) {
            while (1) {
                REP(i,n) visited[i] = 0;
                if (!findFlow(S, INF_FLOW)) break;
            }
            if (!modifyLabel()) break;
        }
        return make_pair(totalFlow, totalCost);
    }

private:
    void SPFA() {
        REP(i,n) dis[i] = INF_COST;
        priority_queue< pair<Cost,int> > Q;
        Q.push(make_pair(dis[S]=0, S));
        while (!Q.empty()) {
            int x = Q.top().second;
            Cost d = -Q.top().first;
            Q.pop();
            // For double: dis[x] > d + EPS
            if (dis[x] != d) continue;
            for(int it = last[x]; it >= 0; it = edges[it].next)
                if (edges[it].cap > 0 && dis[edges[it].to] > d + edges[it].cost)
                    Q.push(make_pair(-(dis[edges[it].to] = d + edges[it].cost), edges[it].to));
        }
        REP(i,n) dis[i] = dis[T] - dis[i];
    }

    Flow findFlow(int x, Flow flow) {
        if (x == T) {
            totalCost += dis[S] * flow;
            totalFlow += flow;
            return flow;
        }
        visited[x] = 1;
        Flow now = flow;
        for(int it = last[x]; it >= 0; it = edges[it].next)
            // For double: fabs(dis[edges[it].to] + edges[it].cost - dis[x]) < EPS
            if (edges[it].cap && !visited[edges[it].to] && dis[edges[it].to] + edges[it].cost == dis[x]) {
                Flow tmp = findFlow(edges[it].to, min(now, edges[it].cap));
                edges[it].cap -= tmp;
                edges[it ^ 1].cap += tmp;
                now -= tmp;
                if (!now) break;
            }
        return flow - now;
    }

    bool modifyLabel() {
        Cost d = INF_COST;
        REP(i,n) if (visited[i])
            for(int it = last[i]; it >= 0; it = edges[it].next)
                if (edges[it].cap && !visited[edges[it].to])
                    d = min(d, dis[edges[it].to] + edges[it].cost - dis[i]);

        // For double: if (d > INF_COST / 10)     INF_COST = 1e20
        if (d == INF_COST) return false;
        REP(i,n) if (visited[i])
            dis[i] += d;
        return true;
    }
};


const int MN = 111;

int x[MN];
int c[MN][MN];

int main() {
    ios :: sync_with_stdio(0); cin.tie(0);
    freopen("rentacar.in", "r", stdin);
    freopen("rentacar.out", "w", stdout);
    int n, m;
    while (cin >> n >> m) {
        memset(x, 0, sizeof x);
        int s = 0, t = n + 1;
        MinCostFlow<int,ll> flow(t+1);

        int suma = 0;
        FOR(i,1,n) {
            int a, b; cin >> a >> b;
            x[i] += a;
            x[i] -= b;

            if (x[i] > 0) suma += x[i];

            if (x[i] > 0) flow.addEdge(s, i, x[i], 0);
            else if (x[i] < 0) flow.addEdge(i, t, -x[i], 0);
        }
        FOR(i,1,n) FOR(j,1,n) c[i][j] = (i == j) ? 0 : 1e9;

        while (m--) {
            int u, v, cost; cin >> u >> v >> cost;
            c[u][v] = min(c[u][v], cost);
            c[v][u] = c[u][v];
        }
        FOR(k,1,n) FOR(i,1,n) FOR(j,1,n)
            c[i][j] = min(c[i][j], c[i][k] + c[k][j]);

        FOR(i,1,n) FOR(j,1,n)
            if (i != j && c[i][j] < 1e9) {
                flow.addEdge(i, j, 10111, c[i][j]);
            }

        auto p = flow.minCostFlow(s, t);
        if (p.first != suma) cout << -1 << endl;
        else cout << p.second << endl;
    }
}