[Graph] baekjoon-1854

Author: Seogeurim

README.md

@@ -179,6 +179,7 @@
 | 03  |     | [Baekjoon-1753 최단경로](./src/Graph/P1753)        |   Dijkstra   |
 | 04  |     | [Baekjoon-11657 타임머신](./src/Graph/P11657)        |   Bellman-Ford   |
 | 05  |     | [Baekjoon-11404 플로이드](./src/Graph/P11404)        |   Floyd-Warshall   |
+| 06  |     | [Baekjoon-1854 K번째 최단경로 찾기](./src/Graph/P1854)   |   Dijkstra   |
 
 ### Union-Find
 

src/Graph/P1854/Main.java

@@ -0,0 +1,70 @@
+package Graph.P1854;
+
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    static int n, m, k;
+    static ArrayList<Node>[] graph;
+    static PriorityQueue<Integer>[] D;
+
+    public static void main(String[] args) throws Exception {
+        System.setIn(new FileInputStream("src/Graph/P1854/input.txt"));
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        n = stoi(st.nextToken());
+        m = stoi(st.nextToken());
+        k = stoi(st.nextToken());
+
+        graph = new ArrayList[n+1];
+        D = new PriorityQueue[n+1];
+        for (int i = 1; i <= n; i++) {
+            graph[i] = new ArrayList<>();
+            D[i] = new PriorityQueue<>(((o1, o2) -> o2 - o1));
+        }
+
+        while (m-- > 0) {
+            st = new StringTokenizer(br.readLine());
+            int a = stoi(st.nextToken()), b = stoi(st.nextToken()), c = stoi(st.nextToken());
+            graph[a].add(new Node(b, c));
+        }
+
+        PriorityQueue<Node> pq = new PriorityQueue<>(((o1, o2) -> o1.dist - o2.dist));
+        pq.offer(new Node(1, 0));
+        D[1].offer(0);
+
+        while (!pq.isEmpty()) {
+            Node cur = pq.poll();
+            for (Node next : graph[cur.idx]) {
+                if (D[next.idx].size() < k) {
+                    D[next.idx].offer(cur.dist + next.dist);
+                    pq.offer(new Node(next.idx, cur.dist + next.dist));
+                } else {
+                    if (D[next.idx].peek() > cur.dist + next.dist) {
+                        D[next.idx].poll();
+                        D[next.idx].offer(cur.dist + next.dist);
+                        pq.offer(new Node(next.idx, cur.dist + next.dist));
+                    }
+                }
+            }
+        }
+
+        for (int i = 1; i <= n; i++) {
+            if (D[i].size() < k) System.out.println(-1);
+            else System.out.println(D[i].peek());
+        }
+    }
+
+    static class Node {
+        int idx, dist;
+
+        public Node(int idx, int dist) {
+            this.idx = idx;
+            this.dist = dist;
+        }
+    }
+
+    static int stoi(String s) { return Integer.parseInt(s); }
+}

src/Graph/P1854/README.md

@@ -0,0 +1,11 @@
+## [baekjoon-1854] K번째 최단경로 찾기
+
+![image](https://user-images.githubusercontent.com/22045163/106920032-068dd300-674e-11eb-81d0-e3f362577bcc.png)
+
+### 풀이 로직
+
+다익스트라 알고리즘은 현재 계산된 최단 거리보다 큰 값이 들어오면 무시해버린다. 
+이 문제는 그 값을 무시하지 않고 top `K` 를 뽑는 것이다. 어떻게 이런 생각을 했을까. 
+참 재밌는 다익스트라 🧘🏼‍♂️
+
+![image](https://user-images.githubusercontent.com/22045163/106920894-d266e200-674e-11eb-9e49-c85bd39be790.png)

src/Graph/P1854/input.txt

@@ -0,0 +1,18 @@
+5 10 2
+1 2 2
+1 3 7
+1 4 5
+1 5 6
+2 4 2
+2 3 4
+3 4 6
+3 5 8
+5 2 4
+5 4 1
+
+//output
+-1
+10
+7
+5
+14