题解：AT_abc381_c [ABC381C] 11/22 Substring

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/*Code by Block_Fish
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*/
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#include <bits/stdc++.h>
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#define INF 0x3f3f3f3f
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#define EPS 1e-8
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#define FOR(i, l, r) for (int(i) = (l); (i) <= (r); ++(i))
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#define log printf
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#define IOS                      \
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  ios::sync_with_stdio(false); \
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  cin.tie(nullptr);            \
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  cout.tie(nullptr);
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using namespace std;
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typedef __int128 i128;
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typedef long long ll;
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typedef pair<int, int> PII;
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int n, ans;
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string s;
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template <typename T>
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inline T read() {
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  T sum = 0, fl = 1;
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  char ch = getchar();
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  for (; !isdigit(ch); ch = getchar())
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    if (ch == '-') fl = -1;
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  for (; isdigit(ch); ch = getchar()) sum = sum * 10 + ch - '0';
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  return sum * fl;
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}
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template <typename T>
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inline void write(T x) {
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  if (x < 0) {
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    putchar('-'), write<T>(-x);
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    return;
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  }
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  static T sta[35];
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  int top = 0;
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  do { sta[top++] = x % 10, x /= 10; } while (x);
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  while (top) putchar(sta[--top] + 48);
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}
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int main() {
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  IOS;
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  cin >> n >> s;
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  for (int i = 0; i < n; ++i) {
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    if (s[i] == '/') {
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      int l = i - 1, r = i + 1, len = 1;
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      while (l >= 0 && r < n)
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        if (s[l] == '1' && s[r] == '2') --l, ++r, len += 2;  // 左右同时寻找，所以是 +2
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        else break;  // 不满足了及时break
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      ans = max(ans, len);
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    }
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  }
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  write<int>(ans);
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  return 0;
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}