[JAVA-자바] 1238번: 파티

 

소스코드:

import java.io.BufferedReader;
import java.io.BufferedWriter;
import java.io.IOException;
import java.io.InputStreamReader;
import java.io.OutputStreamWriter;
import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
import java.util.PriorityQueue;
import java.util.StringTokenizer;

public class Main {
    static BufferedReader br;
    static BufferedWriter bw;

    static int N, M, X;
    static List<List<Node>> graph;
    static List<List<Node>> graph_reverse;

    public static class Node {
        int to;
        int cost;

        Node(int t, int c) {
            this.to = t;
            this.cost = c;
        }
    }


    public static void main(String[] args) throws IOException {
        br = new BufferedReader(new InputStreamReader(System.in));
        bw = new BufferedWriter(new OutputStreamWriter(System.out));

        StringTokenizer st = new StringTokenizer(br.readLine());
        N = Integer.parseInt(st.nextToken());
        M = Integer.parseInt(st.nextToken());
        X = Integer.parseInt(st.nextToken());

        graph = new ArrayList<>();
        graph_reverse = new ArrayList<>();

        for (int i = 0; i <= N; i++) {
            graph.add(new ArrayList<>());
            graph_reverse.add(new ArrayList<>());
        }

        for (int i = 0; i < M; i++) {
            st = new StringTokenizer(br.readLine());
            int start = Integer.parseInt(st.nextToken());
            int to = Integer.parseInt(st.nextToken());
            int cost = Integer.parseInt(st.nextToken());

            graph.get(start).add(new Node(to, cost));
            graph_reverse.get(to).add(new Node(start, cost));
        }
        br.close();

        int[] gogo = dijkstra(X, graph_reverse);
        int[] back = dijkstra(X, graph);

        int result = 0;
        for (int i = 1; i <= N; i++) {
            int calc = gogo[i] + back[i];
            result = Math.max(result, calc);
        }

        bw.write(result + "\n");
        bw.close();
    }

    public static int[] dijkstra(int start, List<List<Node>> g) {
        int[] distance = new int[N + 1];
        Arrays.fill(distance, Integer.MAX_VALUE);
        distance[start] = 0;

        PriorityQueue<int[]> pq = new PriorityQueue<>(((o1, o2) -> o1[1] - o2[1]));
        pq.add(new int[]{start, distance[start]});

        while (!pq.isEmpty()) {
            int[] cur = pq.poll();
            int cur_node = cur[0];
            int cur_distance = cur[1];

            if (cur_distance > distance[cur_node]) {
                continue;
            }

            for (Node near : g.get(cur_node)) {
                int next = near.to;
                int cost = near.cost;

                if (distance[next] > distance[cur_node] + cost) {
                    distance[next] = distance[cur_node] + cost;
                    pq.add(new int[]{next, distance[next]});
                }
            }
        }

        return distance;
    }
}

 

글의 내용 중 잘못된 점이나 수정이 필요한 부분, 혹은 궁금한 사항이 있다면 언제든 댓글로 남겨주시면 감사하겠습니다.

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