[20251127] BOJ / G3 / Social Distancing

Ukj0ng/202511/27 BOJ G3 Social Distancing.md

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+```
+import java.io.*;
+import java.util.*;
+
+public class Main {
+    private static final BufferedReader br = new BufferedReader(new InputStreamReader(System.in));
+    private static final BufferedWriter bw = new BufferedWriter(new OutputStreamWriter(System.out));
+    private static final long INF = (long)1e18;
+    private static long[][] grass;
+    private static int N, M;
+    public static void main(String[] args) throws IOException {
+        init();
+        long answer = binarySearch();
+
+        bw.write(answer + "\n");
+        bw.flush();
+        bw.close();
+        br.close();
+    }
+
+    private static void init() throws IOException {
+        StringTokenizer st = new StringTokenizer(br.readLine());
+        N = Integer.parseInt(st.nextToken());
+        M = Integer.parseInt(st.nextToken());
+
+        grass = new long[M][2];
+
+        for (int i = 0; i < M; i++) {
+            st = new StringTokenizer(br.readLine());
+            grass[i][0] = Long.parseLong(st.nextToken());
+            grass[i][1] = Long.parseLong(st.nextToken());
+        }
+
+        Arrays.sort(grass, (o1, o2) -> Long.compare(o1[0], o2[0]));
+    }
+
+    public static long binarySearch() {
+        long left = 0;
+        long right = INF;
+        long result = -1;
+
+        while (left <= right) {
+            long mid = left + (right - left) / 2;
+
+            if (valid(mid)) {
+                result = mid;
+                left = mid + 1;
+            } else {
+                right = mid - 1;
+            }
+        }
+
+        return result;
+    }
+
+    private static boolean valid(long target) {
+        long count = 0;
+        long pos = -INF;
+
+        for (long[] e : grass) {
+            long nextPos = pos + target;
+
+            if (nextPos > e[1]) continue;
+
+            nextPos = Math.max(nextPos, e[0]);
+
+            long canPlace = (e[1] - nextPos) / target + 1;
+            count += canPlace;
+
+            pos = nextPos + (canPlace - 1) * target;
+        }
+
+        return count >= N;
+    }
+}
+```