1

#include <bits/stdc++.h>
using namespace std;
int main()
{
    for (int i = 1000; i <= 9999; i++)
    {
        int a = i % 10;
        int b = i / 10 % 10;
        int c = i / 100 % 10;
        int d = i / 1000 % 10;
        int ii = sqrt(i);
        if (a == b && c == d && a != c && ii * ii == i)
            cout << i << "\n";
    }
    return 0;
}

2

#include <bits/stdc++.h>
using namespace std;
int main()
{
    for (int a = 1; a <= 9; a++)
    {
        for (int b = 0; b <= 9; b++)
        {
            int i = a * 1100 + b * 11; // aabb
            int ii = sqrt(i);
            if (a != b &&
                ii * ii == i)
                cout << i << "\n";
        }
    }
    return 0;
}

3

#include <bits/stdc++.h>
using namespace std;
int main()
{
    for (int i = 1; i <= 10000; i++)
    {
        int ii = i * i;
        int a = ii % 10;
        int b = ii / 10 % 10;
        int c = ii / 100 % 10;
        int d = ii / 1000 % 10;
        if (1000 <= ii && ii <= 9999 &&
            a == b && c == d && a != c)
        {
            cout << ii << "\n";
        }
    }
    return 0;
}