문제 추가

Author: jdalma

number-of-connected-components-in-an-undirected-graph/jdalma.kt

@@ -0,0 +1,63 @@
+import org.assertj.core.api.Assertions;
+import org.junit.jupiter.api.DisplayName;
+import org.junit.jupiter.api.Test;
+
+import java.util.HashSet;
+import java.util.Set;
+
+public class CountConnectedComponents {
+
+    public int countComponents(int n, int[][] edges) {
+        final int[] relation = new int[n];
+        for (int i = 0; i < n ; i++) {
+            relation[i] = i;
+        }
+
+        int result = n;
+        for (int[] edge : edges) {
+            if (union(relation, edge) == 1) {
+                result--;
+            }
+        }
+
+        return result;
+    }
+
+    private int union(int[] relation, int[] edge) {
+        int parent1 = find(relation, edge[0]);
+        int parent2 = find(relation, edge[1]);
+
+        if (parent1 == parent2) {
+            return 0;
+        }
+
+        if (parent1 < parent2) {
+            relation[parent2] = parent1;
+        } else {
+            relation[parent1] = parent2;
+        }
+        return 1;
+    }
+
+    private int find(int[] relation, int node) {
+        int result = node;
+        while (relation[result] != result) {
+            relation[result] = relation[relation[result]];
+            result = relation[result];
+        }
+        return result;
+    }
+
+    @Test
+    @DisplayName("입력받은 노드와 간선을 통해 그래프의 개수를 반환한다")
+    void graphCount() {
+        int actual = countComponents(3, new int[][]{ {0,1}, {0,2} });
+        Assertions.assertThat(actual).isEqualTo(1);
+
+        int actual1 = countComponents(6, new int[][]{ {0,1}, {1,2}, {2,3}, {4,5} });
+        Assertions.assertThat(actual1).isEqualTo(2);
+
+        int actual2 = countComponents(6, new int[][]{ {0,1}, {2,3}, {4,5}, {1,2}, {3,4} });
+        Assertions.assertThat(actual2).isEqualTo(1);
+    }
+}