[20251123] PGM / Lv2 / 소수 찾기 / 이강현

lkhyun/202511/23 PGM Lv2 소수 찾기.md

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+```java
+import java.util.*;
+class Solution {
+    static int[] number;
+    static boolean[] visited;
+    static int len;
+    static Set<Integer> primes = new HashSet<>();
+
+    public int solution(String numbers) {
+        len = numbers.length();
+        number = new int[len];
+        visited = new boolean[len];
+        primes.clear();
+
+        for(int i = 0; i < len; i++){
+            number[i] = Character.getNumericValue(numbers.charAt(i));
+        }
+
+        findPrime(new StringBuilder());
+        return primes.size();
+    }
+
+    public static void findPrime(StringBuilder sb){
+        if(sb.length() > 0){
+            int num = Integer.parseInt(sb.toString());
+            if(isPrime(num)){
+                primes.add(num);
+            }
+        }
+
+        for(int i = 0; i < len; i++){
+            if(!visited[i]){
+                visited[i] = true;
+                sb.append(number[i]);
+                findPrime(sb);
+                sb.deleteCharAt(sb.length() - 1);
+                visited[i] = false;
+            }
+        }
+    }
+
+    public static boolean isPrime(int num){
+        if(num < 2) return false;
+        if(num == 2) return true;
+        if(num % 2 == 0) return false;
+
+        for(int i = 3; i * i <= num; i += 2){
+            if(num % i == 0) return false;
+        }
+        return true;
+    }
+}
+```