o2.cpp

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*/                              
#include<bits/stdc++.h>
using namespace std;
 
#define fastio ios_base::sync_with_stdio(0); cin.tie(0)
#define LL long long 
#define mod 1000000007 
#define all(v) v.begin(),v.end()
#define pr(v) pair<v,v>
#define pb push_back
#define FOR(i, j, k) for (auto i=j ; i<k ; i++)
#define ROF(i, j, k) for (auto i=j ; i>=k ; i--) 
#define debug(...) fprintf(stderr, __VA_ARGS__), fflush(stderr)
#define time__(d) for(long blockTime = 0; (blockTime == 0 ? (blockTime=clock()) != 0 : false); debug("%s time : %.4fs", d, (double)(clock() - blockTime) / CLOCKS_PER_SEC))

const long long INF = 1e18;
const long long MAX = 2e5+10;
int n,q,m;
vector<pair<int,int>>adj[MAX];

void dijkstra(int u, vector<int>&d){
    d[u]=0;
    set<pair<int,int>>s;
    s.insert({u,0});
    while(!s.empty()){
        int p  = s.begin()->first;
        s.erase(s.begin());
        for(auto v : adj[p]){
            int to = v.first;
            int w =  v.second;
            if(w+d[p]<d[to]){
                s.erase({to,d[to]});
                d[to] = w+d[p];
                s.insert({to,d[to]});
            }
        }
    }
}

int main(){
    fastio;
    int t=1;// cin>>t;
    while(t--){
        cin>>n>>m>>q;
        FOR(i,0,m) {
            int x,y,d; cin>>x>>y>>d;
            adj[x].push_back({y,d});
        }
        while(q--){
            int a,b; cin>>a>>b;
            vector<int>d(n+1,INT_MAX);
            dijkstra(a,d);
            if(d[b]==INT_MAX) cout<<-1<<"\n";
            else cout<<d[b]<<"\n";
        }

    }
}