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D - Guess The String
https://codeforces.com/contest/1697/submission/160389890
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Codeforces/1697/D/D.cpp
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66
Codeforces/1697/D/D.cpp
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#include <iostream>
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#include <algorithm>
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#include <string>
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#include <vector>
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using std::cin;
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using std::cout;
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using std::endl;
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const int N = 1e4 + 5;
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int n, a[N], b[N], lst[N];
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int query1(int x) {
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char res;
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cout << "? 1 " << x << endl;
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cin >> res;
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return res - 'a' + 1;
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}
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int query2(int l, int r) {
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int res;
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cout << "? 2 " << l << ' ' << r << endl;
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cin >> res;
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return res;
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}
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int main() {
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std::ios::sync_with_stdio(false);
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cin.tie(nullptr);
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cin >> n;
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lst[a[1] = query1(1)] = 1;
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for (int i = 2; i <= n; i++) {
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int cnt = 0;
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for (int j = 1; j <= 26; j++) {
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if (lst[j]) b[++cnt] = lst[j];
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}
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std::sort(b + 1, b + 1 + cnt);
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int l = 1, r = cnt, res = 0;
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while (l <= r) {
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int mid = l + r >> 1;
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if (query2(b[mid], i) == cnt - mid + 1) {
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res = mid;
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l = mid + 1;
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} else {
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r = mid - 1;
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}
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}
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lst[a[i] = res ? a[b[res]] : query1(i)] = i;
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}
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cout << "! ";
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for (int i = 1; i <= n; i++) {
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cout << char(a[i] - 1 + 'a');
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}
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cout << endl;
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return 0;
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}
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