20251004 baekjoon

code_study/Baekjoon/java/_1043.java

@@ -0,0 +1,77 @@
+import java.util.Scanner;
+import java.lang.reflect.Array;
+import java.util.ArrayList;
+import java.util.stream.IntStream;
+
+class UnionFind {
+    private int [] data;
+
+    UnionFind(int N) {
+        this.data = IntStream.rangeClosed(0, N).toArray();
+    }
+
+    public int find(int x) {
+        if(this.data[x] != x) {
+            return this.data[x] = this.find(this.data[x]);
+        }
+
+        return this.data[x];
+    }
+
+    public void union(int a, int b) {
+        int rootA = this.find(a);
+        int rootB = this.find(b);
+
+        if(rootA != rootB) {
+            if(rootA < rootB) this.data[rootB] = rootA;
+            else this.data[rootA] = rootB;
+        }
+    }
+
+    public void setRoot(int index, int root) {
+        this.data[index] = root;
+    }
+}
+
+public class _1043 {
+    public static void main(String[] args) {
+        Scanner sc = new Scanner(System.in);
+
+        int N = sc.nextInt();
+        UnionFind uf = new UnionFind(N);
+
+        int M = sc.nextInt();
+
+        int truthNum = sc.nextInt();
+        int[] truthGroup = new int[truthNum];
+        for(int i=0; i<truthNum; i++) {
+            truthGroup[i] = sc.nextInt();
+            uf.setRoot(truthGroup[i], 0);
+        }
+
+        @SuppressWarnings("unchecked")
+        ArrayList<Integer>[] partyInfo = new ArrayList[M]; // 2중 ArrayList로 선언해도 되지만 제네릭 배열타입 연습을 위해 이 방법을 이용함.
+        for(int i=0; i<M; i++) {
+            partyInfo[i] = new ArrayList<>();
+            int personNum = sc.nextInt();
+            for(int j=0; j<personNum; j++) {
+                partyInfo[i].add(sc.nextInt());
+            }
+        }
+
+        sc.close();
+
+        for (ArrayList<Integer> party : partyInfo) {
+            for(int i=1; i<party.size(); i++) {
+                uf.union(party.get(0), party.get(i));
+            }
+        }
+
+        int canLie = 0;
+        for (ArrayList<Integer> party : partyInfo) {
+            if(uf.find(party.get(0)) != 0) canLie++;
+        }
+
+        System.out.println(canLie);
+    }
+}