a

一个字符串，出现在一个地方的字符，不能再第二个地方出现

A A A A Z A A A A A AAAAZAAAAA AAAAZAAAAA -———NO
F F G Z Z Z Y FFGZZZY FFGZZZY -—————— YES

#include<bits/stdc++.h>
#define ll long long 
using namespace std;
const int N = 1e4;
int u[N+10], s[N+10];
void solve()
{ 
    int n; cin >> n; 
    string str; cin >> str;
    if (n == 1) puts("YES"),return;
    char ch;
    for (int i = 0; i < n; i++)
    { 
        if (str[i] != str[i+1]) 
        { 
            ch = str[i]; // find the first different index
            for (int j = i+1; j < n; j++) 
            { 
                if (str[i] == str[j]) puts("NO"), return;
            }
        }
    }
    puts("YES");
}
int main()
{ 
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    int T; cin >> T;
    while (T--) 
        solve();
    return 0;
}

b

1到n共有多少位数都相同的数

位数相同的数 1 2 3…9, 11, 22…111…11111…

暴力，肯定是不行的
虽然是div3，否则还不如给大家布置c++课后作业？

#include<bits/stdc++.h>
#define ll long long
using namespace std;
ll fun (int a, int b)
{ 
    ll ans = 0;
    int cnt = 1;
    for (int i = 1; i <= a; ++i){ 
        ans += cnt * b;
        cnt *= 10;
    }
    return ans;
}
void solve()
{ 
    ll n, ans = 0; cin >> n;
    for (int i = 1; i <= 9; ++i) 
        for (int j = 1; j <= 9; ++j) 
            if (fun(i , j) <= n) ans++;
    cout << ans << endl;
}
int main()
{ 
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    int T; cin >> T;
    while (T--)
        solve();
    return 0;
}

或者可以打表

int paiduan(int n)
{ 
    int count=0;
    if(n<10)return n;
    else if(n<=100)
    { 
        n=n/11;
        return 9+n;
    }
    else if(n<=1000)
    { 
        n=n/111;
        return 18+n;
    }
    else if(n<=10000)
    { 
        n=n/1111;
        return 27+n;
    }
    else if(n<=100000)
    { 
        n=n/11111;
        return 36+n;
    }
    else if(n<=1000000)
    { 
        n=n/111111;
        return 45+n;
    }
    else if(n<=10000000)
    { 
        n=n/1111111;
        return 54+n;
    }
    else if(n<=100000000)
    { 
        n=n/11111111;
        return 63+n;
    }
    else
    { 
        n=n/111111111;
        return 72+n;
    }
}

c

输入一个数n
上下左右四个值相差大于1

#include<bits/stdc++.h>
using namespace std;
void solve()
{ 
    int n; cin >> n;
    if (n == 2) { 
        cout << "-1\n";
    } else { 
        for (int i = 1; i <= n * n; i += 2) { 
             cout << i << ' ';
             if ((i + 1) % n == 0) cout << endl;
        }
        for (int i = 2; i <= n * n; i += 2) { 
             cout << i << ' ';
             if ((i + 1) % n == 0) cout << endl;
        }
    }
}
int main()
{ 
    ios_base::sync_with_stdio(false);
    cin.tie(nullptr); cout.tie(nullptr);
    int T; cin >> T;
    while (T--)
        solve();
    return 0;
}