排它平方数

#include <iostream>

using namespace std;

int st[10];
long long n;

void dfs(int k) {
  if(k==6) {
    if(n==203879) return;
    long long cnt=n*n;
    int flag=1;
    while(cnt) {
      if(st[cnt%10]) {
        flag=0;
        break;
      }
      cnt/=10;
    }
    if(flag) {
      cout<<n<<endl;
      exit(0);
    }
    return;
  }
  for(int i=0;i<10;i++) {
    if(!k&&!i) continue;
    if(!st[i]) {
        st[i]=1; n=n*10+i;
        dfs(k+1);
        n/=10; st[i]=0;
    }
  }
}

int main()
{
  dfs(0);
  return 0;
}

买不到的数目

#include <iostream>
#include <vector>

using namespace std;

vector<int>res(2);
int q[100010];

int main()
{
  for(int i=0;i<2;i++) cin>>res[i],q[res[i]]=1;
  for(int i=0;i<2;i++) {
    for(int j=res[i];j<100010;j++) {
      q[j]|=q[j-res[i]];
    }
  }
  for(int i=100009;i>=0;i--) {
    if(!q[i]) {
      cout<<i<<endl;
      exit(0);
    }
  }
  return 0;
}

回文日期

#include <iostream>
#include <algorithm>
#include <string>

using namespace std;

int n;
int days[] = { 0,31,28,31,30,31,30,31,31,30,31,30,31 };

string rev(string ch) {
    reverse(ch.begin(), ch.end());
    return ch;
}

bool check(int k) {
    string res = to_string(k);
    return res == rev(res);
}

bool check_(int k) {
    string res = to_string(k);
    int a = res[0], b = res[1];
    if(a==b) return false;
    return res[2] == a && res[5] == a && res[7] == a && res[3] == b && res[4] == b && res[6] == b;
}

bool check_date(int k) {
    int day = k % 100;
    int month = (k % 10000) / 100;
    int year = k / 10000;
    if (month == 2) {
        if (year % 400 == 0 || (year % 100 != 0 && year % 4 == 0)) return day <= 28;
        else return day <= 29;
    }
    if(month>12) return false;
    return day <= days[month];
}

int main()
{
    cin >> n;
    int flag = 0;
    for (int i = n + 1;; i++) {
        if(!check_date(i)) continue;
        if (!flag && check(i)) {
            cout << i << endl;
            flag = 1;
        }
        if (check_(i)) {
            cout << i << endl;
            break;
        }
    }
    return 0;
}

约瑟夫环

#include <iostream>
using namespace std;
int cal(int sum,int n,int num) {
  if(num==1) return (sum+n-1)%sum;
  return (cal(sum-1,n,num-1)+n)%sum;
}
int main()
{
  int n,m;
  cin>>n>>m;
  cout<<cal(n,m,n)+1<<endl;
  return 0;
}