Codeforces Round 906 (Div. 2)

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 
 
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;
        else
            b = 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;
}
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B

模拟一遍，如果s不行看t能否救s

#include 
 
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;
}
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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 
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);
            else
                res.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;
}
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