L-Trominos

#include <bits/stdc++.h>

using namespace std;
int h, w;

char arr[105][105];

int main() {
  ios_base::sync_with_stdio(0); cin.tie(0);
  cin>>h>>w;
  bool swapped = false;
  bool okay = (h % 3 == 0) && (w % 2 == 0);
  if (!okay) {
    swap(h, w);
    swapped = true;
  }
  
  okay = (h % 3 == 0) && (w % 2 == 0);
  if (!okay && swapped) return cout<<"IMPOSSIBLE\n", 0;
  
  for (int y = 0; y < h; y += 3) {
    for (int x = 0; x < w; x += 2) {
      // draw L downwards
      bool isB = false;
      
      if (y > 0) {
        isB = arr[y-1][x] == 'B';
      } else if (y == 0) {
        isB = arr[y][x-1] == 'A';
      }
      
      char a = 'A';
      char b = 'B';
      
      if (isB) {
        a = 'C';
        b = 'D';
      }
      
      // fill
      arr[y][x] = a;
      arr[y][x+1] = a;
      arr[y+1][x] = a;
      
      arr[y+1][x+1] = b;
      arr[y+2][x] = b;
      arr[y+2][x+1] = b;
    }
  }
  
  if (!swapped) {
    for (int y = 0; y < h; y++) {
      for (int x = 0; x < w; x++) {
        cout<<arr[y][x];
      }
      cout<<"\n";
    }
  } else {
    for (int x = 0; x < w; x++) {
      for (int y = 0; y < h; y++) {
        cout<<arr[y][x];
      }
      cout<<"\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: WRONG ANSWER

Test 38

Verdict: WRONG ANSWER

Test 39

Verdict: ACCEPTED

Test 40

Verdict: ACCEPTED

Test 41

Verdict: ACCEPTED

Test 42

Verdict: ACCEPTED

Test 43

Verdict: WRONG ANSWER

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: WRONG ANSWER

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: WRONG ANSWER

Test 82

Verdict: ACCEPTED

Test 83

Verdict: ACCEPTED

Test 84

Verdict: ACCEPTED

Test 85

Verdict: ACCEPTED

Test 86

Verdict: ACCEPTED

Test 87

Verdict: WRONG ANSWER

Test 88

Verdict: ACCEPTED

Test 89

Verdict: ACCEPTED

Test 90

Verdict: ACCEPTED

Test 91

Verdict: ACCEPTED