input:
1000000000000000000

output:
524638269999999991

optimized search + cross product)

To read the input in C++, the following helped me: unsigned char x = cin.get().

Then I used some ifs in the form of if (x == 218) { ... }

Also, the first test case seems to be different from the one suggested in the statement.

b = input()
s = ''
d = []
for i in b:
    s += i
    if s == s[::-1]:
        d.append(s)
    if s != s[::-1] and len(s) % 2 != 0:
        s = s[1:]
    if s == s[::-1]:
        d.append(s)
    if s != s[::-1] and len(s) % 2 != 0:
        s = s[1:]
m = max(d, key=len)
if len(m) <= 1000:
    print(m)

see what your program outputs for an integer answer
ps it should output .00

посмотрите, что выводит ваша программа при целом ответе
ps она должна выводить .00

1 5
/\/\X
.\X\\
ans: 4

#include <bits/stdc++.h>
using namespace std;

int cal(int x){
    int ret = 0;
    while (x > 0){
        ret += x % 10;
        x /= 10;
    }
    return ret;
}

bool lucky(int x, int mm){
    int a = x / mm;
    int b = x % mm;
    if (cal(a) == cal(b)) return true;
    return false;
}

int main(){
    int n;
    cin >> n;
    int nn = round(pow(10, n)) - 1;
    int mm = round(pow(10, n / 2));
    int tot = 0;
    for (int i = 0; i <= nn; i++){
        if (lucky(i, mm)) tot++;
    }
    cout << tot << endl;
}

if your code is simple and fast enough, brute force can work.

what is wrong with my code:

#include <iostream>
#include <algorithm>
#include <climits>
#include <string>
#include <cstring>
#include <cmath>
#include <vector>
#include <stack>
#include <map>
#include <set>
#include <iomanip>
#include <unordered_map>
#define ll long long
#define fri(a, b) for (ll i = a; i < b; i++)
#define frj(a, b) for (ll j = a; j < b; j++)
#define frk(a, b) for (int k = a; k < b; k++)
#define frh(a, b) for (int h = a; h < b; h++)
#define frz(a, b) for (int z = a; z < b; z++)
#define rfri(a, b) for (int i = a; i >= b; i--)
#define rfrj(a, b) for (int j = a; j >= b; j--)
#define yes cout << "YES" << "\n";
#define no cout << "NO" << "\n";
#define fast                          \
    ios_base::sync_with_stdio(false); \
    cin.tie(NULL);                    \
    cout.tie(NULL);
const int mod=100000007;
using namespace std;
ll dp[50][1005];

ll func(ll n,ll s){
  if(dp[n][s] != -1) return dp[n][s];
  if(s == 0) return 1;
  if(n == 0){
    if(s == 0) return 1;
    else return 0;
  }
  ll ans = 0;
  fri(0,10){
    if((s - i) >= 0) ans = (ans + func(n-1,s-i)) ;
  }
  return dp[n][s] = ans;
}

int main() {
    fast
    ll T = 1;
    // cin >> T;

    frz(0,T){
      ll n,s;
      cin >> n >> s;
      memset(dp,-1,sizeof(dp));
      if(s%2) cout << 0 << "\n";
      else {
        ll ans = func(n,s/2);
        cout << (ans*ans) << "\n";
      }
    }
}

For example:
16
9001 9001
8999 8999
9001 8999
8999 9001
-9001 -9001
-9001 -8999
-8999 -9001
-8999 -8999
9001 -9001
8999 -8999
9001 -8999
8999 -9001
-9001 9001
-8999 8999
-9001 8999
-8999 9001
5
9000 9000
9000 -9000
-9000 -9000
-9000 9000
0 0

My AC program gives answer:
1 2 3 4
9 10 11 12
5 6 7 8
13 14 15 16
2

But right answer:
1 2 3 4
9 10 11 12
5 6 7 8
13 14 15 16
2 8 10 14

Hi, Admins.
Please, add these case:
N > 5*10^4
a[i] = 1, for i = 1.. N-1, and
a[N] = 10^9

Q = N
p[i] = i,  x[i] = i

For example:
77888
1 1 1 1 1 1 .... 1 1 77888
77888
1 1
2 2
3 3
4 4
5 5
...
77888 77888

my solution takes 0.031 seconds.

I tried with precalculating with map for setting up the index with 1 only rest will be auto 0 but miraculously WA at 4. so i figured out that the author only wants you to solve with his idea only. So good luck.

DO your own solve then check this do not cheat yourself
#include<bits/stdc++.h>
using namespace std;
#define ll long long
#define endl "\n"
#define FastAF ios_base::sync_with_stdio(false);cin.tie(0);cout.tie(0);

template <typename T> // cin >> vector<T>
istream &operator>>(istream &istream, vector<T> &v){for (auto &it : v) cin >> it;return istream;}
template <typename T> // cout << vector<T>
ostream &operator<<(ostream &ostream, const vector<T> &c){for (auto &it : c) cout << it << " ";return ostream;}

const int mx=2e5;

int ar[mx];
void d(){
    ar[0]=2;
    int k=1;
    for(int i=3;i<mx;i++){
        bool f=true;
        for(int j=2;j*j<=i;j++){
            if(i%j==0){
                f=false;
                break;
            }
        }
        if(f){
            ar[k++]=i;
        }
    }
}

int main(){
    FastAF
    d();
    int n;
    cin>>n;
    while(n--){
        int a;cin>>a;
        cout<<ar[--a]<<endl;
    }
return 0;
}

Algo: sqrt with precomputation

Edited by author 11.05.2025 11:58

Edited by author 11.05.2025 12:02

6
0 0 0 0 12 40
ANS: 52

8 7

0 0
16
1 1
2 1
2 0
3 0
3 1
2 2
3 2
4 1
4 3
0 3
0 4
1 4
1 5
-1 5
-1 -1
1 -1
12.00000000000000000000

0 0
5
-1 -1
1 0
0 -1
2 -2
2 4
5.50000000000000000000

0 0
17
-1 -1
5 -1
1 0
1 1
2 2
2 1
3 1
3 3
4 4
4 3
5 3
5 5
0 5
0 6
6 6
6 7
-1 7
24.00000000000000000000

0 0
4
0 -1
1 0
0 1
-1 0
2.00000000000000000000

0 0
4
-1 2
-1 -1
1 0
3 -1
3.6666666666

0 0
3
-1 -1
1 -1
0 1
2.00000000000000000000

0 0
11
0 -1
3 0
2 2
1 1
2 3
0 4
0 3
-1 5
-2 3
0 2
-1 0
10.50000000000000000000

I would appreciate hints(or solution) a lot!

Please e-mail me at addflash@dmc.chat

Why is the sample 50.211, shouldn't the sample be 50.198 because the path (45, 0) -> (50, 1) -> (5, 1) -> (0, 0) is length 50.198?

Is there some constructive approach? I solved it with some tricky bruteforce with optimizations