Merge pull request #1719 from AlgorithmWithGod/LiiNi-coder

[20251220] BOJ / G4 / 특정한 최단 경로 / 이인희

Author: ShinHeeEul

LiiNi-coder/202512/20 BOJ 특정한 최단 경로.md

@@ -0,0 +1,80 @@
+```java
+import java.io.*;
+import java.util.*;
+
+public class Main {
+	static class Edge {
+		int to;
+		int cost;
+		Edge(int to, int cost){
+			this.to = to;
+			this.cost = cost;
+		}
+	}
+
+	static final int INF = 100_000_000;
+	static ArrayList<Edge>[] Graph;
+
+	public static void main(String[] args) throws IOException {
+		BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+		StringTokenizer st = new StringTokenizer(br.readLine());
+		int N = Integer.parseInt(st.nextToken());
+		int E = Integer.parseInt(st.nextToken());
+
+		Graph = new ArrayList[N + 1];
+		for(int i = 1; i <= N; i++){
+			Graph[i] = new ArrayList<>();
+		}
+		for(int i = 0; i < E; i++){
+			st = new StringTokenizer(br.readLine());
+			int a = Integer.parseInt(st.nextToken());
+			int b = Integer.parseInt(st.nextToken());
+			int c = Integer.parseInt(st.nextToken());
+			Graph[a].add(new Edge(b, c));
+			Graph[b].add(new Edge(a, c));
+		}
+		st = new StringTokenizer(br.readLine());
+		int A = Integer.parseInt(st.nextToken());
+		int B = Integer.parseInt(st.nextToken());
+		int[] dist1 = dikstra(1, N);
+		int[] distA = dikstra(A, N);
+		int[] distB = dikstra(B, N);
+
+		long path1 = (long)dist1[A] + distA[B] + distB[N];
+		long path2 = (long)dist1[B] + distB[A] + distA[N];
+		long answer = Math.min(path1, path2);
+		System.out.println((answer >= INF) ? -1 : answer);
+	}
+
+	private static int[] dikstra(int start, int N){
+		int[] dist = new int[N + 1];
+		Arrays.fill(dist, INF);
+		dist[start] = 0;
+
+		PriorityQueue<int[]> pq = new PriorityQueue<>(
+			(a, b) -> a[1] - b[1]
+		);
+		pq.offer(new int[]{start, 0});
+
+		while(!pq.isEmpty()){
+			int[] cur = pq.poll();
+			int now = cur[0];
+			int cost = cur[1];
+
+			if(cost > dist[now])
+				continue;
+
+			for(Edge e : Graph[now]){
+				int next = e.to;
+				int nextCost = cost + e.cost;
+				if(nextCost < dist[next]){
+					dist[next] = nextCost;
+					pq.offer(new int[]{next, nextCost});
+				}
+			}
+		}
+		return dist;
+	}
+}
+
+```