[20250211] BOJ / 골드4 / 전기요금 / 이강현

lkhyun/202502/11 BOJ 골드4 전기요금.md

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+```java
+import java.util.*;
+import java.io.*;
+
+public class Main {
+    static int A;
+    static int B;
+    static int totalUse;
+
+    public static void main(String[] args) throws Exception {
+        BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+        BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+        StringTokenizer st = new StringTokenizer(br.readLine());
+
+        while (st.hasMoreTokens()) {
+            A = Integer.parseInt(st.nextToken()); // 총 사용량에 기반한 요금
+            B = Integer.parseInt(st.nextToken()); // 요금 차이
+            if (A == 0 && B == 0) break;
+
+            totalUse = convertToUse(A); // 총 사용량(상한)
+            int use1 = binarySearch(0, totalUse); // 상근이의 사용 요금
+            int use2 = totalUse-use1;
+            bw.write(Math.min(convertToFee(use1),convertToFee(use2)) +"\n");
+            st = new StringTokenizer(br.readLine());
+        }
+
+        bw.flush();
+    }
+
+    public static int binarySearch(int left, int right) {
+        while (left <= right) {
+            int mid = (left + right) / 2;
+            int sangeunFee = convertToFee(mid);
+            int nextToFee = convertToFee(totalUse - mid);
+
+            if (Math.abs(nextToFee - sangeunFee) == B) return mid;
+            else if (Math.abs(nextToFee - sangeunFee) < B) right = mid - 1;
+            else left = mid + 1;
+        }
+        return left;
+    }
+
+    public static int convertToFee(int use) { // 사용량 -> 요금
+        if (use > 1000000) return 4979900 + (use - 1000000) * 7;
+        if (use > 10000) return 29900 + (use - 10000) * 5;
+        if (use > 100) return 200 + (use - 100) * 3;
+        return use * 2;
+    }
+
+    public static int convertToUse(int fee) { // 요금 -> 사용량
+        if (fee > 4979900) return 1000000 + (fee - 4979900) / 7;
+        if (fee > 29900) return 10000 + (fee - 29900) / 5;
+        if (fee > 200) return 100 + (fee - 200) / 3;
+        return fee / 2;
+    }
+}
+
+```