Backtrack almost working

python_prototype/backtrack.py

@@ -0,0 +1,119 @@
+#!/usr/bin/env python3
+
+import os
+import sys
+
+PADDING = int(os.popen('tput cols').read()) // 3 # '// 2 - 6' for exact middle for n=4
+
+def get_board_dim(board: list) -> int:
+    return int(len(board) ** 0.5)
+
+def get_row(board: list, pos: int) -> list:
+    board_dim = get_board_dim(board)
+    row_start = pos // board_dim * board_dim
+    row = board[
+        row_start
+        :
+        row_start + board_dim
+        :
+        1
+    ]
+    return row
+
+def get_col(board: list, pos: int) -> list:
+    board_dim = get_board_dim(board)
+    column_start = pos % board_dim
+    column = board[
+        column_start
+        :
+        board_dim**2 - (board_dim - column_start) + 1
+        :
+        board_dim
+    ]
+    return column
+
+def get_candidates(board: list, next_candidate_index: int) -> int:
+    all_candidates = set(range(1 + get_board_dim(board)))
+    row = get_row(board, next_candidate_index)
+    column = get_col(board, next_candidate_index)
+
+    for candidate in all_candidates.copy():
+        if candidate in row:
+            all_candidates.discard(candidate)
+            continue
+        if candidate in column:
+            all_candidates.discard(candidate)
+            continue
+    return all_candidates
+
+def get_constraints(board: list, border: list, pos: int) -> list:
+    pass
+
+def is_valid_state(board: list, border: list, next_candidate_index: int) -> bool:
+    board_dim = get_board_dim(board)
+    print_board(board, border)
+    row = get_row(board, next_candidate_index)
+    column = get_col(board, next_candidate_index)
+    constraints = get_constraints(board, border, next_candidate_index)
+    print(constraints, row, column)
+    return True
+
+def print_board(board: list, border: list) -> None:
+    padding = ' ' * PADDING
+    board_dim = get_board_dim(board)
+    print(end=padding + '  ')
+    print(' '.join(border[:board_dim]))
+    for i in range(board_dim):
+        print(end=padding + border[i + board_dim * 2] + '|')
+        for j in range(board_dim):
+            print(board[j + i * board_dim], end=' ')
+        print(end='\b|')
+        print(end=border[i + board_dim * 3])
+        print(end='\b\n')
+    print(end=padding + '  ')
+    print(' '.join(border[board_dim:board_dim * 2]))
+    print()
+
+def backtrack(board: list, sols: list, border: list) -> None:
+    if board.count(0) == 0:
+        sols.append(board)
+        print("Solutions")
+        print_board(sols[0], border)
+        print("Done")
+        sys.exit(0)
+    next_candidate_index = board.index(0)
+    candidates = get_candidates(board, next_candidate_index)
+    for candidate in candidates:
+        board[next_candidate_index] = candidate
+        if is_valid_state(board, border, next_candidate_index):
+            backtrack(board, sols, border)
+            continue
+
+def main(*args, **kwargs) -> None:
+
+    if kwargs:
+        print('Error (kwargs)')
+        sys.exit(1)
+    if len(args) != 1:
+        print('Error (args)')
+        sys.exit(2)
+
+    try:
+        border = args[0].split()
+    except:
+        print('Error (could not split)')
+        sys.exit(3)
+    board_dim = len(border) / 4
+    if board_dim != int(board_dim):
+        print('Board is not square')
+        sys.exit(4)
+    else:
+        board_dim = int(board_dim)
+
+    board = [
+        0 for _ in range(board_dim ** 2)
+    ]
+    number_of_sols = backtrack(board, [], border)
+
+if __name__ == '__main__':
+    sys.exit(main('4 3 2 1 1 2 2 2 4 3 2 1 1 2 2 2'))