CF-1004-C. Devyatkino · znzryb

## 思路讲解

[https://codeforces.com/blog/entry/139415?locale=en](https://codeforces.com/blog/entry/139415?locale=en)

![image](https://media.znzryb.com/20250212-cf0d3e30/image_45b2f613.png)

就只看最后一位数（因为最后一位数不会有进位什么的问题），就可以得到最多不会超过9次的结论

然后就直接暴力就好了，不知道题解后面在写什么

## AC代码

[https://codeforces.com/contest/2067/submission/305782258](https://codeforces.com/contest/2067/submission/305782258)

```cpp
// Problem: C. Devyatkino
// Contest: Codeforces - Codeforces Round 1004 (Div. 2)
// URL: https://codeforces.com/contest/2067/problem/C
// Memory Limit: 256 MB
// Time Limit: 2000 ms
// by znzryb
//
// Powered by CP Editor (https://cpeditor.org)

#include <bits/stdc++.h>
#define FOR(i, a, b) for (int i = (a); i <= (b); ++i)
#define ROF(i, a, b) for (int i = (a); i >= (b); --i)
#define all(x) x.begin(), x.end()
#define CLR(i, a) memset(i, a, sizeof(i))
#define fi first
#define se second
#define pb push_back
#define SZ(a) ((int)a.size())
#define LOCAL

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef pair<ll, ll> pll;
typedef array<ll, 3> arr;
typedef double DB;
typedef pair<DB, DB> pdd;
constexpr ll MAXN = static_cast<ll>(1e6) + 10, INF = static_cast<ll>(5e18) + 3;

ll N, T;
ll pow10[20];

inline void solve() {
  ll x;
  cin >> x;
  ll ans = 9;
  string s = to_string(x);
  N = SZ(s);
  FOR(i, 0, N - 1) {
    if (s[i] == '7') {
      cout << 0 << '\n';
      return;
    }
  }
  FOR(i, 1, N + 1) {
    ll add = pow10[i] - 1;
    ll t = x;
    FOR(j, 1, ans) {
      t += add;
      string ts = to_string(t);
      bool isBreak = false;
      FOR(k, 0, SZ(ts) - 1) {
        if (ts[k] == '7') {
          ans = j;
          // #ifdef LOCAL
          // FOR(lk, 0, SZ(ts) - 1) { cerr << ts[lk]; }
          // cerr << '\n';
          // #endif
          isBreak = true;
          break;
        }
      }
      if (isBreak) break;
    }
  }
  cout << ans << '\n';
}

int main() {
  ios::sync_with_stdio(false);
  cin.tie(0);
  cout.tie(0);
  cin >> T;
  pow10[0] = 1;
  FOR(i, 1, 18) { pow10[i] = pow10[i - 1] * 10; }
  while (T--) {
    solve();
    // #ifdef LOCAL
    // cerr << '\n';
    // #endif
  }
  return 0;
}
/*
AC
https://codeforces.com/contest/2067/submission/305782258
*/
```

## 心路历程（WA，TLE，MLE……）