[20250711] BOJ / G2 / 1의 개수 세기 / 이인희

Author: LiiNi-coder

LiiNi-coder/202507/11 BOJ 1의 개수 세기.md

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+# 코드
+```java
+import java.io.BufferedReader;
+import java.io.IOException;
+import java.io.InputStreamReader;
+import java.math.BigInteger;
+
+public class Main {
+    private static BufferedReader br;
+
+    public static void main(String[] args) throws IOException {
+        br = new BufferedReader(new InputStreamReader(System.in));
+        String[] temp1 = br.readLine().split(" ");
+        BigInteger l = new BigInteger(temp1[0]);
+        BigInteger r = new BigInteger(temp1[1]);
+
+        BigInteger result = BigInteger.ZERO;
+
+        for (int exponent = 0; exponent <= 63; exponent++) {
+            BigInteger blockSize = BigInteger.ONE.shiftLeft(exponent);
+            if (blockSize.compareTo(r) > 0) break;
+
+            BigInteger lBlockIdx = l.divide(blockSize);
+            BigInteger rBlockIdx = r.divide(blockSize);
+
+            if (lBlockIdx.equals(rBlockIdx)) {
+                if (getBitAtBlock(lBlockIdx)) {
+                    result = result.add(r.subtract(l).add(BigInteger.ONE));
+                }
+            } else {
+                if (getBitAtBlock(lBlockIdx)) {
+                    BigInteger lEnd = blockSize.multiply(lBlockIdx.add(BigInteger.ONE));
+                    result = result.add(lEnd.subtract(l));
+                }
+                if (getBitAtBlock(rBlockIdx)) {
+                    BigInteger rStart = blockSize.multiply(rBlockIdx);
+                    result = result.add(r.subtract(rStart).add(BigInteger.ONE));
+                }
+
+                // C
+                BigInteger offsetBlock = rBlockIdx.subtract(lBlockIdx).subtract(BigInteger.ONE);
+                BigInteger half = offsetBlock.divide(BigInteger.TWO);
+                if (offsetBlock.mod(BigInteger.TWO).equals(BigInteger.ZERO)) {
+                    result = result.add(blockSize.multiply(half));
+                } else {
+                    if (getBitAtBlock(rBlockIdx)) {
+                        result = result.add(blockSize.multiply(half));
+                    } else {
+                        result = result.add(blockSize.multiply(half).add(blockSize));
+                    }
+                }
+            }
+        }
+
+        System.out.println(result);
+        br.close();
+    }
+
+    private static boolean getBitAtBlock(BigInteger idx) {
+        return idx.mod(BigInteger.TWO).equals(BigInteger.ONE);
+    }
+}
+
+```
+
+#결과
+맞았습니다!!	14484kB	104ms