[20251216] PGM / LV2 / 소수 찾기 / 이인희

LiiNi-coder/202512/16 PGM 소수 찾기.md

@@ -0,0 +1,56 @@
+```java
+import java.util.*;
+
+class Solution {
+    private static boolean[] visited;
+    private static HashSet<Integer> set;
+    private static char[] nums;
+
+    public int solution(String numbers) {
+        nums = numbers.toCharArray();
+        visited = new boolean[nums.length];
+        set = new HashSet<>();
+
+
+        dfs("", 0);
+        int answer = 0;
+        for(int n : set){
+            if(isPrime(n)){
+                answer++;
+            }
+        }
+        return answer;
+    }
+
+    private void dfs(String now, int depth){
+        if(now.length() > 0){
+            set.add(Integer.parseInt(now));
+        }
+        if(depth == nums.length){
+            return;
+        }
+
+        for(int i = 0; i < nums.length; i++){
+            if(visited[i]){
+                continue;
+            }
+            visited[i] = true;
+            dfs(now + nums[i], depth + 1); // String + char 가능
+            visited[i] = false;
+        }
+    }
+
+    private boolean isPrime(int n){
+        if(n < 2){
+            return false;
+        }
+        for(int i = 2; i <= n / 2; i++){
+            if(n % i == 0){
+                return false;
+            }
+        }
+        return true;
+    }
+}
+
+```