[20250504] BOJ / G4 / 특정한 최단 경로 / 이강현

Author: lkhyun

lkhyun/202505/04 BOJ G4 특정한 최단 경로.md

@@ -0,0 +1,83 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    static class Node {
+        int to,cost;
+        Node(int to, int cost) {
+            this.to = to;
+            this.cost = cost;
+        }
+    }
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static int N,E;
+    static List<Node>[] adjList;
+    static int v1,v2;
+    static int MAX = Integer.MAX_VALUE;
+    static int min = -1;
+
+    public static void main(String[] args) throws Exception {
+        st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        E = Integer.parseInt(st.nextToken());
+        adjList = new ArrayList[N+1];
+        for (int i = 1; i <= N; i++) {
+            adjList[i] = new ArrayList<>();
+        }
+        for (int i = 0; i < E; i++) {
+            st = new StringTokenizer(br.readLine());
+            int from = Integer.parseInt(st.nextToken());
+            int to = Integer.parseInt(st.nextToken());
+            int cost = Integer.parseInt(st.nextToken());
+            adjList[from].add(new Node(to, cost));
+            adjList[to].add(new Node(from, cost));
+        }
+        st = new StringTokenizer(br.readLine());
+        v1 = Integer.parseInt(st.nextToken());
+        v2 = Integer.parseInt(st.nextToken());
+        int[][] dist = new int[3][N+1];
+        dijkstra(1,dist[0]);
+        dijkstra(v1,dist[1]);
+        dijkstra(v2,dist[2]);
+
+        boolean flag1 = true;
+        boolean flag2 = true;
+        if(dist[0][v1] == MAX || dist[1][v2] == MAX || dist[2][N] == MAX) flag1 = false;
+        if(dist[0][v2] == MAX || dist[2][v1] == MAX || dist[1][N] == MAX) flag2 = false;
+        if(flag1 && flag2){
+            min = Math.min(dist[0][v1] + dist[1][v2] + dist[2][N],dist[0][v2] + dist[2][v1] + dist[1][N]);
+        }else if(flag1){
+            min = dist[0][v1] + dist[1][v2] + dist[2][N];
+        }else if(flag2){
+            min = dist[0][v2] + dist[2][v1] + dist[1][N];
+        }
+        bw.write(min + "");
+        bw.close();
+    }
+    public static void dijkstra(int start , int[] dist) {
+        PriorityQueue<Node> pq = new PriorityQueue<>((a,b) -> a.cost - b.cost);
+        pq.add(new Node(start,0));
+        Arrays.fill(dist,MAX);
+        dist[start] = 0;
+
+        while (!pq.isEmpty()) {
+            Node cur = pq.poll();
+
+            if(cur.cost > dist[cur.to]) {
+                continue;
+            }
+            for(Node n : adjList[cur.to]){
+                int newDist = dist[cur.to] + n.cost;
+                if(newDist < dist[n.to]) {
+                    dist[n.to] = newDist;
+                    pq.add(new Node(n.to,newDist));
+                }
+            }
+        }
+    }
+
+}
+```