Programación Competitiva

#include <bits/stdc++.h>
#define INF 0x3F3F3F3F
using namespace std;

const int MAXN = 1005;

struct edge{
  int from, to, weight;
  edge(){}
  edge(int a, int b, int c){
    from = a;
    to = b;
    weight = c;
  }
};

struct state{
  int node, dist;
  state(){}
  state(int a, int b){
    node = a; dist = b;
  }
  bool operator<(const state &other)const{ 
    return other.dist < dist;
  }
};

vector<edge> graph[MAXN];
int dist[MAXN];

int a=1, b=3;
int N,E;

int dijkstra(int start, int end){
  dist[start] = 0;
  priority_queue<state> pq;
  pq.push(state(start, 0));
  while(!pq.empty()){
    state cur = pq.top(); pq.pop();
    if(dist[cur.node] < cur.dist) continue;
    if(cur.node == end) return cur.dist;
    for(int i=0;i<graph[cur.node].size();i++){
      int dest = graph[cur.node][i].to;
      int wht = graph[cur.node][i].weight + cur.dist;
      if(dist[dest] <= wht) continue;
      dist[dest] = wht;
      pq.push(state(dest, wht));
    }
  }
  return -1;
}
int main(){
  while(scanf("%d",&N)!=EOF)
  {
    int arr[N];
    for(int i =0; i<N;i++) cin>>arr[i];
    scanf("%d",&E);
    memset(dist,INF,sizeof(dist));
    for(int i=0;i<=N;i++) { graph[i].clear(); } // limpia el grafo
    for(int i=0;i<E;i++){
    int from, to, weight; scanf("%d %d %d",&from, &to, &weight);
    to--; from--;
    graph[from].push_back(edge(from,to,weight+arr[to]));
    }
    int res = dijkstra(0,N-1);
    if (res==-1) printf("IMPOSIBLE\n");
    else printf("%d\n",res+arr[0]);
  }
  return 0;
}