[20250919] BOJ / G1 / K번째 수 / 이강현

lkhyun/202509/19 BOJ G1 K번째 수.md

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+```java
+import java.util.*;
+import java.io.*;
+
+public class Main{
+    static BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    static BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    static StringTokenizer st;
+    static StringBuilder sb = new StringBuilder();
+    static long N,K;
+
+    public static void main(String[] args) throws Exception {
+        N = Integer.parseInt(br.readLine());
+        K = Integer.parseInt(br.readLine());
+        bw.write(binarySearch(1, N*N) +"");
+        bw.close();
+    }
+    public static long binarySearch(long start, long end){
+        long left = start;
+        long right = end;
+        long mid = 0;
+        while (left <= right) {
+            mid = (left + right) / 2;
+
+            long smaller = 0;
+            long equal = 0;
+
+            for (int i = 1; i <= N; i++) {
+                long maxJ = mid / i;
+
+                if (maxJ > N) maxJ = N;
+
+                if (mid % i == 0 && mid / i <= N) {
+                    smaller += maxJ - 1;
+                    equal++;
+                } else {
+                    smaller += maxJ;
+                }
+            }
+
+            if (smaller >= K) {
+                right = mid - 1;
+            } else if (smaller + equal >= K) {
+                return mid;
+            } else {
+                left = mid + 1;
+            }
+        }
+        return mid;
+    }
+}
+```