git reimport

archive/2016.09/2016.09.19 - unsorted/M.java

@@ -0,0 +1,78 @@
+package chelper;
+
+import java.util.Arrays;
+import java.util.LinkedList;
+import java.util.Queue;
+
+import io.InputReader;
+import io.OutputWriter;
+
+public class M {
+  boolean ask(InputReader in, OutputWriter out, int i, int j) {
+    out.println("? " + i + " " + j);
+    out.flush();
+    return in.nextLine().charAt(0) == '<';
+  }
+
+  public void solve(int testNumber, InputReader in, OutputWriter out) {
+    int n = Integer.parseInt(in.nextLine());
+
+    int m = Integer.highestOneBit(n) * 2;
+    int[] a = new int[2 * m];
+    Arrays.fill(a, -1);
+
+    for (int i = 0; i < n; i++) {
+      a[m + i] = i + 1;
+    }
+
+    for (int i = m - 1; i >= 1; i--) {
+      int c1 = a[2 * i];
+      int c2 = a[2 * i + 1];
+
+      if (c2 == -1 || c1 == -1) {
+        a[i] = c1;
+        continue;
+      }
+
+      a[i] = ask(in, out, c1, c2) ? c2 : c1;
+    }
+
+    int p = 1;
+
+    Queue<Integer> candidates = new LinkedList<>();
+
+    while (true) {
+      int c1 = p * 2;
+      int c2 = p * 2 + 1;
+
+      if (c1 >= 2 * m || c2 >= 2 * m) {
+        break;
+      }
+
+      if (a[c2] == a[p]) {
+        int t = c1;
+        c1 = c2;
+        c2 = t;
+      }
+
+      if (a[c2] != -1) {
+        candidates.add(a[c2]);
+      }
+      p = c1;
+    }
+
+    while (candidates.size() > 1) {
+      int a1 = candidates.poll();
+      int a2 = candidates.poll();
+
+      if (ask(in, out, a1, a2)) {
+        candidates.add(a2);
+      } else {
+        candidates.add(a1);
+      }
+    }
+
+    out.println("! " + candidates.poll());
+    out.flush();
+  }
+}