Modern art

input/code.cpp: In function 'void solve()':
input/code.cpp:88:23: warning: comparison of integer expressions of different signedness: 'long long int' and 'std::vector<std::__cxx11::basic_string<char> >::size_type' {aka 'long unsigned int'} [-Wsign-compare]
   88 |     for (int i = 0; i < output.size(); i++)
      |                     ~~^~~~~~~~~~~~~~~

#include <iostream>
#include <vector>
#include <array>
#include <string>
#include <algorithm>
#include <numeric>
#include <unordered_map>
#include <unordered_set>
#include <queue>
#include <climits>
#include <cmath>
#include <functional>
#include <type_traits>
#include <fstream>
#include <bitset>
#include <complex>
#include <iomanip>
 
#define int long long
using namespace std;
 
//#define cross(x, y) ((x).real()*(y).imag()-(x).imag()*(y).real()) 
#define cross(x, y) (((x)*conj(y)).imag())
#define sign(v) ((0 < (v)) - ((v) < 0))

void solve()
{
    int a, p;
    cin >> a >> p;
 
    if (p % 2 == 1)
    {
        cout << "IMPOSSIBLE";
        return;
    }
    int inputtedBlockCount = 0;

    vector<string> output;

    int needed = p / 2 - 1;
    int hor = (needed+1) / 2;
    int ver = needed - hor; // Start from 1

    int stillNeeded = a - needed;

    int width = hor + 2;
    output.push_back(string(width, '0'));

    // First line
    output.push_back(string());
    output[1].push_back('0');
    for (int i = 0; i < hor; i++)
    {
        output[1].push_back('1');
        inputtedBlockCount++;
    }
    output[1].push_back('0');

    for (int i = 2; i <= ver+1; i++)
    {
        output.push_back(string());
        output[i].push_back('0');
        output[i].push_back('1');
        inputtedBlockCount++;
        int c = 0;
        for (; stillNeeded > 0 && c < hor-1; c++)
        {
            output[i].push_back('1');
            inputtedBlockCount++;
            stillNeeded--;
        }
        for (; c < hor-1; c++)
            output[i].push_back('0');

        output[i].push_back('0');
    }
    
    
    output.push_back(string(width, '0'));

    if (inputtedBlockCount != a)
    {
        cout << "IMPOSSIBLE";
        return;
    }

    cout << "POSSIBLE" << '\n';
    for (int i = 0; i < output.size(); i++)
    {
        cout << output[i] << '\n';
    }
}
 
 
signed main()
{
    ios::sync_with_stdio(0);
    cout.precision(25);
    //setprecision(10);
    //cin.tie(0);
 
    int t = 1;
 
    //cin >> t;
    //ifstream f("testcase.txt");
    //cin.rdbuf(f.rdbuf());
 
    for (int i = 0; i < t; i++)
        solve();
}

Test 1

Verdict: ACCEPTED

Test 2

Verdict: ACCEPTED

Test 3

Verdict: ACCEPTED

Test 4

Verdict: ACCEPTED

Test 5

Verdict: ACCEPTED

Test 6

Verdict: ACCEPTED

Test 7

Verdict: ACCEPTED

Test 8

Verdict: ACCEPTED

Test 9

Verdict: ACCEPTED

Test 10

Verdict: ACCEPTED

Test 11

Verdict: ACCEPTED

Test 12

Verdict: ACCEPTED

Test 13

Verdict: ACCEPTED

Test 14

Verdict: ACCEPTED

Test 15

Verdict: ACCEPTED

Test 16

Verdict: ACCEPTED

Test 17

Verdict: ACCEPTED

Test 18

Verdict: ACCEPTED

Test 19

Verdict: ACCEPTED

Test 20

Verdict: ACCEPTED

Test 21

Verdict: ACCEPTED

Test 22

Verdict: ACCEPTED

Test 23

Verdict: ACCEPTED

Test 24

Verdict: ACCEPTED

Test 25

Verdict: ACCEPTED

Test 26

Verdict: ACCEPTED

Test 27

Verdict: ACCEPTED

Test 28

Verdict: ACCEPTED

Test 29

Verdict: ACCEPTED

Test 30

Verdict: ACCEPTED

Test 31

Verdict: ACCEPTED

Test 32

Verdict: ACCEPTED

Test 33

Verdict: ACCEPTED

Test 34

Verdict: ACCEPTED

Test 35

Verdict: ACCEPTED

Test 36

Verdict: ACCEPTED

Test 37

Verdict: ACCEPTED

Test 38

Verdict: ACCEPTED

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: ACCEPTED

Test 44

Verdict: ACCEPTED

Test 45

Verdict: ACCEPTED

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED