[백인찬] 후보키

solution/Programmers_후보키/백인찬.java

@@ -0,0 +1,99 @@
+
+import java.util.*;
+
+class Solution {
+    static String[][] table;
+    static int columns;
+    static boolean[] uniqueness;
+
+    static boolean[] selected;
+    static class Pair {
+        List<Integer> keys;
+
+        public Pair() {
+            keys = new ArrayList<>();
+        }
+    }
+    static List<List<Integer>> compositeKeys;
+
+    public int solution(String[][] relation) {
+        table = relation;
+        columns = table[0].length;
+        compositeKeys = new ArrayList<>();
+        uniqueness = new boolean[columns];
+
+        int answer = 0;
+
+        // uniqueness 체크
+        for (int i = 0; i < columns; i++) {
+            if(checkUniquenessByOne(i)) {
+                uniqueness[i] = true;
+
+                List<Integer> temp = new ArrayList<>();
+                temp.add(i);
+                compositeKeys.add(temp);
+                answer++;
+            }
+        }
+        for (int i = 2; i <= columns; i++) {
+            selected = new boolean[columns];
+            for (int j = 0; j < columns; j++) {
+                if(uniqueness[j]) continue;
+                makeCompositeKey(j, 0, i);
+            }
+        }
+
+
+        return compositeKeys.size();
+    }
+    public static void makeCompositeKey(int now, int count, final int max) {
+        if(count == max) {
+            Pair pair = new Pair();
+            for (int i = 0; i < columns; i++) {
+                if(selected[i]) {
+                    pair.keys.add(i);
+                }
+            }
+            if(checkMinimality(pair)) {
+                if(checkUniquenessByCompositeKey(pair)) {
+                    compositeKeys.add(new ArrayList<>(pair.keys));
+                }
+            }
+        }
+        for (int i = now; i < columns; i++) {
+            if(selected[i]) continue;
+            if(uniqueness[i]) continue;
+            selected[i] = true;
+            makeCompositeKey(now, count + 1, max);
+            selected[i] = false;
+        }
+    }
+
+    public static boolean checkMinimality(Pair pair) {
+        for (List<Integer> key : compositeKeys) {
+            if(pair.keys.containsAll(key)) {
+                return false;
+            }
+        }
+        return true;
+    }
+
+    public static boolean checkUniquenessByCompositeKey(Pair pair) {
+        Set<List<String>> set = new HashSet<>();
+        for (String[] row: table) {
+            List<String> temp = new ArrayList<>();
+            for (int column : pair.keys) {
+                temp.add(row[column]);
+            }
+            set.add(temp);
+        }
+        return set.size() == table.length;
+    }
+    public static boolean checkUniquenessByOne(int column) {
+        Set<String> set = new HashSet<>();
+        for (String[] row : table) {
+            set.add(row[column]);
+        }
+        return set.size() == table.length;
+    }
+}