L-Trominos

#include <bits/stdc++.h>
using namespace std;
int n, m;


char c[5555][5555];


void c1(int x, int y){
  c[x][y]=c[x+1][y]=c[x][y+1]=('A'+4*(x%4)+4*(y%4)+1);
  c[x+2][y]=c[x+2][y+1]=c[x+1][y+1]=('A'+4*(x%4)+4*(y%4)+2);
}
void c2(int x, int y){
  c[x][y]=c[x][y+1]=c[x+1][y]=('A'+4*(x%4)+4*(y%4)+3);
  c[x][y+2]=c[x+1][y+2]=c[x+1][y+1]=('A'+4*(x%4)+4*(y%4)+4);
}

bool fill(int a, int b, int aa, int bb){
  int w=aa-a;
  int h=bb-b;
  if (w%3==0 && h%2==0){
    if (h==2){
      for (int i=a;i<aa;i+=3){
        c1(i, b);
      }
    }else{
      for (int j=b;j<bb;j+=2){
        fill(a, j, aa, j+2);
      }
    }
  }else if (h%3==0 && w%2==0){
    if (w==2){
      for (int j=b;j<bb;j+=3){
        c2(a, j);
      }
    }else{
      for (int i=a;i<aa;i+=2){
        fill(i, b, i+2, bb);
      }
    }
  }else{
    if (h%6==0){
      if (w%3==2 && w>=5){
        fill(a, b, a+2, bb);
        fill(a+2, b, aa, bb);
        return 0;
      }else if (w%3==1 && w>=7){
        fill(a, b, a+2, bb);
        fill(a+2, b, a+4, bb);
        fill(a+4, b, aa, bb);
        return 0;
      }
    }
    if (w%6==0){
      if (h%3==2 && h>=5){
        fill(a, b, aa, b+2);
        fill(a, b+2, aa, bb);
        return 0;
      }else if (h%3==1 && h>=7){
        fill(a, b, aa, b+2);
        fill(a, b+2, aa, b+4);
        fill(a, b+4, aa, b+4);
        return 0;
      }
    }
    return 1;
  }
  return 0;
}

int main(){
  cin >> n >> m;
  if (fill(0, 0, n, m)) cout << "IMPOSSIBLE\n";
  else{
    for (int i=0;i<n;++i){
      cout << c[i] << "\n";
    }
  }
}

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: WRONG ANSWER

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: WRONG ANSWER

Test 46

Verdict: ACCEPTED

Test 47

Verdict: ACCEPTED

Test 48

Verdict: ACCEPTED

Test 49

Verdict: ACCEPTED

Test 50

Verdict: ACCEPTED

Test 51

Verdict: WRONG ANSWER

Test 52

Verdict: ACCEPTED

Test 53

Verdict: ACCEPTED

Test 54

Verdict: ACCEPTED

Test 55

Verdict: ACCEPTED

Test 56

Verdict: ACCEPTED

Test 57

Verdict: ACCEPTED

Test 58

Verdict: ACCEPTED

Test 59

Verdict: WRONG ANSWER

Test 60

Verdict: ACCEPTED

Test 61

Verdict: WRONG ANSWER

Test 62

Verdict: ACCEPTED

Test 63

Verdict: WRONG ANSWER

Test 64

Verdict: ACCEPTED

Test 65

Verdict: ACCEPTED

Test 66

Verdict: ACCEPTED

Test 67

Verdict: ACCEPTED

Test 68

Verdict: ACCEPTED

Test 69

Verdict: ACCEPTED

Test 70

Verdict: ACCEPTED

Test 71

Verdict: ACCEPTED

Test 72

Verdict: WRONG ANSWER

Test 73

Verdict: ACCEPTED

Test 74

Verdict: ACCEPTED

Test 75

Verdict: WRONG ANSWER

Test 76

Verdict: WRONG ANSWER

Test 77

Verdict: WRONG ANSWER

Test 78

Verdict: WRONG ANSWER

Test 79

Verdict: ACCEPTED

Test 80

Verdict: WRONG ANSWER

Test 81

Verdict: ACCEPTED

Test 82

Verdict: ACCEPTED

Test 83

Verdict: ACCEPTED

Test 84

Verdict: ACCEPTED

Test 85

Verdict: ACCEPTED

Test 86

Verdict: ACCEPTED

Test 87

Verdict: ACCEPTED

Test 88

Verdict: ACCEPTED

Test 89

Verdict: ACCEPTED

Test 90

Verdict: ACCEPTED

Test 91

Verdict: ACCEPTED