[백준 20007] 떡 돌리기 - 그래프, 최단경로

Author: HiiWee

hoseok/week79/Boj20007.java

@@ -0,0 +1,82 @@
+import java.io.*;
+import java.util.*;
+
+class Main {
+
+    static int n, m, x, y;
+    static List<int[]>[] graph;
+
+    public static void main(String[] args ) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter 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());
+        y = Integer.parseInt(st.nextToken());
+        graph = new ArrayList[n];
+
+        for (int i = 0; i < n; i++) {
+            graph[i] = new ArrayList<>();
+        }
+
+        for (int i = 0; i < m; 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 int[]{b, c});
+            graph[b].add(new int[]{a, c});
+        }
+
+        int[] dist = dijkstra();
+        Arrays.sort(dist);
+
+        int count = 0;
+        int sum = 0;
+        for (int i = 1; i < n; i++) {
+            if (dist[i] * 2 > x) {
+                bw.write("-1");
+                bw.flush();
+                bw.close();
+                return;
+            }
+            if (sum + dist[i] * 2 <= x) {
+                sum += dist[i] * 2;
+            } else {
+                count++;
+                sum = dist[i] * 2;
+            }
+        }
+        if (sum > 0) {
+            count++;
+        }
+
+        bw.write(Integer.toString(count));
+        bw.flush();
+        bw.close();
+    }
+
+    public static int[] dijkstra() {
+        int[] dist = new int[n];
+        Arrays.fill(dist, 100_000_000);
+        dist[y] = 0;
+
+        PriorityQueue<int[]> pq = new PriorityQueue<>(Comparator.comparingInt(o -> o[1]));
+        pq.offer(new int[]{y, 0});
+
+        while (!pq.isEmpty()) {
+            int[] current = pq.poll();
+
+            for (int[] next : graph[current[0]]) {
+
+                if (dist[next[0]] > current[1] + next[1]) {
+                    dist[next[0]] = current[1] + next[1];
+                    pq.offer(new int[]{next[0], dist[next[0]]});
+                }
+            }
+        }
+
+        return dist;
+    }
+}