Codeforces Round 906 (Div. 2)

A

分类讨论，如果数的总数大于2直接return false,否者看个数差

#include <bits/stdc++.h>const int N = 105;
int a[N];void solve()
{int n;std::cin >> n;std::unordered_map<int, int> m;for (int i = 1; i <= n; i++){std::cin >> a[i];m[a[i]]++;}if (m.size() > 2){std::cout << "No\n";return;}else if (m.size() < 2){std::cout << "Yes\n";return;}int a = 0, b = 0;for (auto x : m){if (a == 0)a = x.second;elseb = x.second;}if (abs(a - b) <= 1){std::cout << "Yes\n";}else{std::cout << "No\n";}
}int main()
{int T;std::cin >> T;while (T--){solve();}return 0;
}

B

模拟一遍，如果s不行看t能否救s

#include <bits/stdc++.h>const int N = 105;
int a[N];bool check(std::string s){int n = s.size();char last = '2';for(int i = 0 ; i < n ; i ++){if(last == '2' || last != s[i]){last = s[i];}else{return false;}}return true;
}void solve()
{int n , m;std::string s , t;    std::cin >> n >> m;std::cin >> s;std::cin >> t;int fi = t[0] , en = t[m - 1];if(check(s)){std::cout << "Yes\n";return ;}if(check(t)){char last = '2';for(int i = 0 ; i < n ; i ++){if(last == '2' || last != s[i]){last = s[i];}else{if(fi != s[i - 1] && en != s[i])continue;else{std::cout << "No\n";return ;}}            }}else{std::cout << "No\n";return ;}std::cout << "Yes\n";
}int main()
{int T;std::cin >> T;while (T--){solve();}return 0;
}

C

左右两个指针向内扫
不等为0的时候插在右边，为1的时候插在左边

#include <bits/stdc++.h>
std::string t = "01";
void solve()
{std::string s;std::vector<int> res;int n;std::cin >> n >> s;int l = 0, r = n - 1;if (n % 2){std::cout << "-1\n";return;}while (l < r){if (s[l] == s[r]){if (s[l] == '0')res.push_back(r + 1), s.insert(r + 1, t);elseres.push_back(l), s.insert(l, t);r += 2;}l++, r--;if (res.size() > 300){std::cout << "-1\n";return;}}std::cout << res.size() << std::endl;for (auto x : res)std::cout << x << " ";std::cout << std::endl;
}int main()
{int T;std::cin >> T;while (T--){solve();}return 0;
}

---