BOJ_3896 : 소수 사이 수열

Author: spring0913

week5/BOJ_3896(소수 사이 수열).java

@@ -0,0 +1,58 @@
+import java.io.*;
+import java.util.*;
+
+public class Main {
+
+    public static final int MAX = 1299710;
+
+    public static void main(String[] args) throws IOException {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        List<Integer> primeNumber = getPrimeNumber();
+        int T = Integer.parseInt(br.readLine());
+        for (int i = 0; i < T; i++) {
+            int num = Integer.parseInt(br.readLine());
+            if (num == 1) {
+                System.out.println('0');
+                continue;
+            }
+            binarySearch(primeNumber, num);
+        }
+    }
+
+    public static void binarySearch(List<Integer> primeNumber, int num) {
+        int left = 0;
+        int right = primeNumber.size() - 1;
+        while (left <= right) {
+            int mid = (left + right) / 2;
+            int primeNum = primeNumber.get(mid);
+            if (num <= primeNum) {
+                right = mid - 1;
+                if (num == primeNum) {
+                    System.out.println('0');
+                    return;
+                }
+            } else {
+                left = mid + 1;
+            }
+        }
+        int answer = primeNumber.get(left) - primeNumber.get(left - 1);
+        System.out.println(answer);
+    }
+
+    public static List<Integer> getPrimeNumber() {
+        boolean[] check = new boolean[MAX];
+        List<Integer> primeNumber = new ArrayList<>();
+        for (int i = 2; i < MAX; i++) {
+            if (check[i]) {
+                continue;
+            }
+            primeNumber.add(i);
+            for (int j = i; j < MAX; j += i) {
+                if (!check[j]) {
+                    check[j] = true;
+                }
+            }
+        }
+        return primeNumber;
+    }
+}