Патарини

package Paytolls;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;
import java.util.*;

class Edge{
    private int fromVertex, toVertex;
    private float weight;
    public Edge(int from, int to, float weight){
        this.fromVertex = from;
        this.toVertex = to;
        this.weight = weight;
    }

    public int getFrom(){
        return this.fromVertex;
    }
    public int getTo(){
        return this.toVertex;
    }
    public float getWeight(){
        return this.weight;
    }

    @Override
    public String toString() {
        return "("+fromVertex+","+toVertex+")="+weight+" ";
    }


}

class GraphNode<E> {
    private int index; //index (reden broj) na temeto vo grafot
    private E info;
    private LinkedList<GraphNodeNeighbor<E>> neighbors;

    public GraphNode(int index, E info) {
        this.index = index;
        this.info = info;
        neighbors = new LinkedList<GraphNodeNeighbor<E>>();
    }

    public boolean containsNeighbor(GraphNode<E> o){
        GraphNodeNeighbor<E> pom = new GraphNodeNeighbor<E>(o,0);
        return neighbors.contains(pom);
    }

    public void addNeighbor(GraphNode<E> o, float weight){
        GraphNodeNeighbor<E> pom = new GraphNodeNeighbor<E>(o,weight);
        neighbors.add(pom);
    }

    public void removeNeighbor(GraphNode<E> o){
        GraphNodeNeighbor<E> pom = new GraphNodeNeighbor<E>(o,0);
        if(neighbors.contains(pom))
            neighbors.remove(pom);
    }

    @Override
    public String toString() {
        String ret= "INFO:"+info+" SOSEDI:";
        for(int i=0;i<neighbors.size();i++)
        ret+="("+neighbors.get(i).node.info+","+neighbors.get(i).weight+") ";
        return ret;

    }

    public void updateNeighborWeight(GraphNode<E> o, float weight){
        Iterator<GraphNodeNeighbor<E>> i = neighbors.iterator();
        while(i.hasNext()){
            GraphNodeNeighbor<E> pom = i.next();
            if(pom.node.equals(o))
                pom.weight = weight;
        }

    }

    @Override
    public boolean equals(Object obj) {
        @SuppressWarnings("unchecked")
        GraphNode<E> pom = (GraphNode<E>)obj;
        return (pom.info.equals(this.info));
    }

    public int getIndex() {
        return index;
    }

    public void setIndex(int index) {
        this.index = index;
    }

    public E getInfo() {
        return info;
    }

    public void setInfo(E info) {
        this.info = info;
    }

    public LinkedList<GraphNodeNeighbor<E>> getNeighbors() {
        return neighbors;
    }

    public void setNeighbors(LinkedList<GraphNodeNeighbor<E>> neighbors) {
        this.neighbors = neighbors;
    }



}

class GraphNodeNeighbor<E> {
    GraphNode<E> node;
    float weight;

    public GraphNodeNeighbor(GraphNode<E> node, float weight) {
        this.node = node;
        this.weight = weight;
    }

    public GraphNodeNeighbor(GraphNode<E> node) {
        this.node = node;
        this.weight = 0;
    }

    @Override
    public boolean equals(Object obj) {
        @SuppressWarnings("unchecked")
        GraphNodeNeighbor<E> pom = (GraphNodeNeighbor<E>)obj;
        return pom.node.equals(this.node);
    }





}

class Graph<E> {

    int num_nodes;
    GraphNode<E> adjList[];

    @SuppressWarnings("unchecked")
    public Graph(int num_nodes, E[] list) {
        this.num_nodes = num_nodes;
        adjList = (GraphNode<E>[]) new GraphNode[num_nodes];
        for (int i = 0; i < num_nodes; i++)
            adjList[i] = new GraphNode<E>(i, list[i]);
    }

    @SuppressWarnings("unchecked")
    public Graph(int num_nodes) {
        this.num_nodes = num_nodes;
        adjList = (GraphNode<E>[]) new GraphNode[num_nodes];
        for (int i = 0; i < num_nodes; i++)
            adjList[i] = new GraphNode<E>(i, null);
    }

    int adjacent(int x, int y) {
        // proveruva dali ima vrska od jazelot so
        // indeks x do jazelot so indeks y
        return (adjList[x].containsNeighbor(adjList[y])) ? 1 : 0;
    }

    void addEdge(int x, int y, float tezina) {
        // dodava vrska od jazelot so indeks x do jazelot so indeks y so tezina
        // i obratno
        if (adjList[x].containsNeighbor(adjList[y])) {
            adjList[x].updateNeighborWeight(adjList[y], tezina);
            adjList[y].updateNeighborWeight(adjList[x], tezina);
        } else{
            adjList[x].addNeighbor(adjList[y], tezina);
            adjList[y].addNeighbor(adjList[x], tezina);
        }
    }

    void deleteEdge(int x, int y) {
        adjList[x].removeNeighbor(adjList[y]);
        adjList[y].removeNeighbor(adjList[x]);
    }

    /*************************** KRUSKAL ***********************************************************************/

    // Metoda koja generira niza od site rebra vo grafot
    public Edge[] getAllEdges() {
        int totalEdges = 0;
        for (int i = 0; i < this.num_nodes; i++) {
            // za sekoe teme go dodavame brojot na sosedi koi gi ima
            totalEdges += this.adjList[i].getNeighbors().size();
        }

        totalEdges /= 2; //bidejki e nenasocen graf, sekoe rebro se javuva kaj dve teminja

        Edge[] edges = new Edge[totalEdges];
        int index = 0;
        for (int i = 0; i < this.num_nodes; i++) {
            for (int j = 0; j < this.adjList[i].getNeighbors().size(); j++) {
                int index1 = this.adjList[i].getIndex();
                // se zemaat indeksot i tezinata na j-ot sosed na temeto i
                int index2 = this.adjList[i].getNeighbors().get(j).node
                        .getIndex();
                float weight = this.adjList[i].getNeighbors().get(j).weight;
                if(index2>index1) //bidejki grafot e nenasocen, da ne go zemame sekoe rebro dva pati
                    edges[index++] = new Edge(index1, index2, weight);
            }
        }

        return edges;
    }

    // Metoda koja gi sortira site rebra
    private void sortEdges(Edge[] edges) {
        for (int i = 0; i < edges.length - 1; i++) {
            for (int j = i + 1; j < edges.length; j++) {
                if (edges[i].getWeight() > edges[j].getWeight()) {
                    Edge tmp = edges[i];
                    edges[i] = edges[j];
                    edges[j] = tmp;
                }
            }
        }

    }

    //Metoda koja pravi unija na dve drva
    private void union(int u, int v, int[] vrski){
        int findWhat, replaceWith;

        if(u < v){
            findWhat = vrski[v];
            replaceWith = vrski[u];
        }
        else{
            findWhat = vrski[u];
            replaceWith = vrski[v];
        }

        //za dvete poddrva stava ist index
        //vo vrski t.e. gi spojuva
        for(int i=0; i<vrski.length; i++){
            if(vrski[i] == findWhat){
                vrski[i] = replaceWith;
            }
        }
    }

    List<Edge> kruskal() {
        /*
         * Pomoshna niza za sledenje na kreiranite drva
         * Ako dve teminja se del od isto poddrvo
         * togash imaat ista vrednost vo nizata
         */
        int vrski[] = new int[this.num_nodes];

        // niza koja gi sodrzi site rebra
        Edge[] edges = this.getAllEdges();
        // se sortiraat rebrata spored tezinite vo neopagjacki redosled
        this.sortEdges(edges);

        // inicijalizacija na pomosnata niza za evidencija,
        // sekoj jazel si e posebno drvo
        for (int i = 0; i < this.num_nodes; i++)
            vrski[i] = i;

        // lista koja kje gi sodrzi MST rebra
        List<Edge> mstEdges = new ArrayList<Edge>();

        for(int i=0; i<edges.length; i++){
            //za sekoe rebro vo sortiran redosled
            Edge e = edges[i];

            if(vrski[e.getFrom()] != vrski[e.getTo()]){
                //ako teminjata na ova rebro ne se vo isto poddrvo
                //ova rebro e MST rebro
                mstEdges.add(e);
                //sega dvete teminja treba da se vo isto poddrvo
                //t.e se pravi merge (unija) t.s. vo nizata vrski
                //za site elementi od dvete poddrva
                //go setira istiot (najmal) element od dvete poddrva
                //vrski = this.union(e.getFrom(), e.getTo(), vrski);
                this.union(e.getFrom(), e.getTo(), vrski);
            }

            //ako sme dodale num_nodes-1 rebra moze da prestaneme
            if(mstEdges.size()==(this.num_nodes-1))
                break;
        }

        return mstEdges;
    }

    /*******************************************************************************************************/
    /************************ PRIM **************************************************************************/

    //Metoda koja go naogja najmaloto rebro do
    //teme na neposeten sosed
    private Edge getMinimalEdge(boolean[] included){
        int index1 = Integer.MAX_VALUE, index2 = Integer.MAX_VALUE;
        float minweight = Float.MAX_VALUE;

        for(int i=0;i<this.num_nodes;i++){
            if(included[i]){
                //ako e vkluceno temeto i
                //izmini gi negovite nevkluceni sosedi
                Iterator<GraphNodeNeighbor<E>> it = adjList[i].getNeighbors().iterator();
                while(it.hasNext()){
                    GraphNodeNeighbor<E> pom = it.next();
                    //ako sosedot ne e poseten i ima do sega najmala tezina
                    if(!included[pom.node.getIndex()] && pom.weight<minweight){
                        index1 = i;
                        index2 = pom.node.getIndex();
                        minweight = pom.weight;
                    }
                }
            }
        }

        if(minweight<Float.MAX_VALUE){
            Edge ret = new Edge(index1, index2, minweight);
            return ret;
        }
        return null;
    }


    List<Edge> prim(int start_index) {
        // lista koja kje gi sodrzi MST rebra
        List<Edge> mstEdges = new ArrayList<Edge>();

        boolean included[] = new boolean[this.num_nodes];
        for(int i=0;i<this.num_nodes;i++)
            included[i]=false;

        included[start_index] = true;

        for(int i=0;i<this.num_nodes-1;i++){
            Edge e = this.getMinimalEdge(included);
            if(e==null){
                System.out.println("Ne mozat da se povrzat site jazli");
                break;
            }
            included[e.getFrom()] = included[e.getTo()] = true;
            mstEdges.add(e);
        }

        return mstEdges;
    }

    /*******************************************************************************************************/
    /***************** DIJKSTRA ******************************************************************************/

    float[] dijkstra(int from) {

        /* Minimalna cena do sekoe od teminjata */
        float distance[] = new float[this.num_nodes];
        /* dali za temeto e najdena konecnata (minimalna) cena */
        boolean finalno[] = new boolean[this.num_nodes];
        for (int i = 0; i < this.num_nodes; i++) {
            distance[i] = -1;
            finalno[i] = false;
        }

        finalno[from] = true;
        distance[from] = 0;

        /*
         * vo sekoj cekor za edno teme se dobiva konecna minimalna cena
         */
        for (int i = 1; i < this.num_nodes; i++) {
            /* za site sledbenici na from presmetaj ja cenata */
            Iterator<GraphNodeNeighbor<E>> it = adjList[from].getNeighbors().iterator();
            while (it.hasNext()) {
                GraphNodeNeighbor<E> pom = it.next();
                /* ako grankata kon sosedot nema konecna cena */
                if (!finalno[pom.node.getIndex()]) {
                    /* ako ne e presmetana cena za temeto */
                    if (distance[pom.node.getIndex()] <= 0) {
                        distance[pom.node.getIndex()] = distance[from]
                                + pom.weight;
                    }
                    /* inaku, ako e pronajdena poniska */
                    else if (distance[from] + pom.weight < distance[pom.node
                            .getIndex()]) {
                        distance[pom.node.getIndex()] = distance[from]
                                + pom.weight;
                    }
                }
            }

            /* najdi teme so min. cena koja ne e konecna */
            boolean minit = false; /* min. ne e inicijaliziran */
            int k = -1;
            float minc = -1;
            /* proveri gi site teminja */
            for (int j = 0; j < this.num_nodes; j++) {
                if (!finalno[j] && distance[j] != -1) { /*ako cenata ne e  konecna*/
                    if (!minit) { /* ako ne e inicijaliziran minimumot */
                        minc = distance[k = j]; /* proglasi go ova e minimum */
                        minit = true; /* oznaci deka min e inicijaliziran */
                    }
                    /* proveri dali e pronajdeno teme so pomala cena */
                    else if (minc > distance[j] && distance[j] > 0)
                        minc = distance[k = j];
                }
            }
            finalno[from = k] = true;
        }

        return distance;

    }

    /*******************************************************************************************************/

    @Override
    public String toString() {
        String ret = new String();
        for (int i = 0; i < this.num_nodes; i++)
            ret += adjList[i] + "\n";
        return ret;
    }

}

public class Paytolls {

    public static void main(String[] args) throws IOException {

        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
        String expr = br.readLine();
        String[] exp;

        int teminja = Integer.parseInt(expr);
        expr = br.readLine();
        exp = expr.split(" ");
        int start = Integer.parseInt(exp[0]) - 1;
        int end = Integer.parseInt(exp[1]) - 1;

        expr = br.readLine();
        int rebra = Integer.parseInt(expr);

        Graph<Integer> g = new Graph<>(teminja);

        for(int i=0; i<rebra; i++){
            expr = br.readLine();
            exp = expr.split(" ");
            int x = Integer.parseInt(exp[0]) - 1;
            int y = Integer.parseInt(exp[1]) - 1;
            float tezina = Float.parseFloat(exp[2]);
            g.adjList[x].setInfo(x);
            g.adjList[y].setInfo(y);
            g.addEdge(x, y, tezina);
        }

        float[] path = g.dijkstra(start);

        System.out.println((int)(path[end]));

        br.close();

    }

}