[20251107] PGM / LV2 / 소수 찾기 / 김민진

zinnnn37/202511/7 PGM LV2 소수 찾기.md

@@ -0,0 +1,65 @@
+```java
+import java.util.Arrays;
+import java.util.HashSet;
+import java.util.Set;
+
+class PGM_LV2_소수_찾기 {
+
+    private static int len;
+    private static String num;
+    private static boolean[] isPrime, visited;
+    private static Set<Integer> set;
+
+    private static void findPrime() {
+        Arrays.fill(isPrime, 2, 10000000, true);
+
+        for (int i = 2; i * i <= 10000000; i++) {
+            if (isPrime[i]) {
+                for (int j = i * i; j < 10000000; j += i) {
+                    isPrime[j] = false;
+                }
+            }
+        }
+    }
+
+    private static void init(String numbers) {
+        num = numbers;
+        len = num.length();
+
+        isPrime = new boolean[10000000];
+        visited = new boolean[len];
+
+        set = new HashSet<>();
+
+        findPrime();
+    }
+
+    private void dfs(int depth, int start, int candidate) {
+        if (depth > len) {
+            return;
+        }
+
+        if (candidate > 0) {
+            if (isPrime[candidate]) {
+                set.add(candidate);
+            }
+        }
+
+        for (int i = 0; i < len; i++) {
+            if (visited[i]) continue;
+
+            int curNum = num.charAt(i) - '0';
+
+            visited[i] = true;
+            dfs(depth + 1, start + 1, candidate * 10 + curNum);
+            visited[i] = false;
+        }
+    }
+
+    public int solution(String numbers) {
+        init(numbers);
+        dfs(0, 0, 0);
+        return set.size();
+    }
+}
+```