[20260204] BOJ / G1 / 냅색문제 / 김민진

zinnnn37/202602/04 BOJ G1 냅색문제.md

@@ -0,0 +1,97 @@
+```java
+import java.io.*;
+import java.util.ArrayList;
+import java.util.Collections;
+import java.util.List;
+import java.util.StringTokenizer;
+
+public class BJ_1450_냅색문제 {
+
+    private static final BufferedReader  br = new BufferedReader(new InputStreamReader(System.in));
+    private static final BufferedWriter  bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    private static       StringTokenizer st;
+
+    private static int N, C;
+    private static int[]      weight;
+    private static List<Long> left, right;
+
+    public static void main(String[] args) throws IOException {
+        init();
+        sol();
+    }
+
+    private static void init() throws IOException {
+        st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        C = Integer.parseInt(st.nextToken());
+
+        weight = new int[N];
+        st = new StringTokenizer(br.readLine());
+        for (int i = 0; i < N; i++) {
+            weight[i] = Integer.parseInt(st.nextToken());
+        }
+
+        left = new ArrayList<>();
+        right = new ArrayList<>();
+    }
+
+    private static void sol() throws IOException {
+        int mid = N / 2;
+
+        int leftBit = (1 << mid);
+        for (int subset = 0; subset < leftBit; subset++) {
+            long sum = 0;
+            for (int idx = 0; idx < mid; idx++) {
+                if ((subset & (1 << idx)) != 0) {
+                    sum += weight[idx];
+                }
+            }
+            if (sum <= C) {
+                left.add(sum);
+            }
+        }
+
+        int rightSize = N - mid;
+        int rightBit  = (1 << rightSize);
+        for (int subset = 0; subset < rightBit; subset++) {
+            long sum = 0;
+            for (int idx = 0; idx < rightSize; idx++) {
+                if ((subset & (1 << idx)) != 0) {
+                    sum += weight[idx + mid];
+                }
+            }
+            if (sum <= C) {
+                right.add(sum);
+            }
+        }
+
+        Collections.sort(right);
+
+        long ans = 0;
+        for (long leftSum : left) {
+            ans += upperBound(right, C - leftSum);
+        }
+
+        bw.write(ans + "");
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+
+    private static int upperBound(List<Long> list, long target) {
+        int start = 0;
+        int end   = list.size();
+
+        while (start < end) {
+            int mid = (start + end) / 2;
+            if (list.get(mid) <= target) {
+                start = mid + 1;
+            } else {
+                end = mid;
+            }
+        }
+        return start;
+    }
+
+}
+```