D - Guess The String

https://codeforces.com/contest/1697/submission/160389890

Codeforces/1697/D/D.cpp

@@ -0,0 +1,66 @@
+#include <iostream>
+#include <algorithm>
+#include <string>
+#include <vector>
+
+using std::cin;
+using std::cout;
+using std::endl;
+
+const int N = 1e4 + 5;
+
+int n, a[N], b[N], lst[N];
+
+int query1(int x) {
+    char res;
+    cout << "? 1 " << x << endl;
+    cin >> res;
+    return res - 'a' + 1;
+}
+
+int query2(int l, int r) {
+    int res;
+    cout << "? 2 " << l << ' ' << r << endl;
+    cin >> res;
+    return res;
+}
+
+int main() {
+    std::ios::sync_with_stdio(false);
+    cin.tie(nullptr);
+
+    cin >> n;
+
+    lst[a[1] = query1(1)] = 1;
+
+    for (int i = 2; i <= n; i++) {
+        int cnt = 0;
+        for (int j = 1; j <= 26; j++) {
+            if (lst[j]) b[++cnt] = lst[j];
+        }
+
+        std::sort(b + 1, b + 1 + cnt);
+
+        int l = 1, r = cnt, res = 0;
+        while (l <= r) {
+            int mid = l + r >> 1;
+
+            if (query2(b[mid], i) == cnt - mid + 1) {
+                res = mid;
+                l = mid + 1;
+            } else {
+                r = mid - 1;
+            }
+        }
+
+        lst[a[i] = res ? a[b[res]] : query1(i)] = i;
+    }
+
+    cout << "! ";
+    for (int i = 1; i <= n; i++) {
+        cout << char(a[i] - 1 + 'a');
+    }
+    cout << endl;
+
+    return 0;
+}