代码

#include <bits/stdc++.h>

using namespace std;

unsigned solve(int n, const char *s) {
  vector<unsigned> dp = {1};
  for (int i = 0; i < n; ++i) {
    vector<unsigned> pd(min(i + 1, n - i - 1) / 2 + 1);
    if (s[i] != ')') {
      if (i & 1) {
        copy_n(dp.begin(), min(pd.size() - 1, dp.size()), pd.begin() + 1);
      } else {
        copy_n(dp.begin(), min(pd.size(), dp.size()), pd.begin());
      }
    }
    if (s[i] != '(') {
      for (int j = i & 1; j / 2 < dp.size(); j += 2) {
        if (j > 0) {
          pd[(j - 1) / 2] += dp[j / 2];
        }
      }
    }
    dp = pd;
  }
  return dp[0];
}

评测结果