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Micro-Drill #185 — N-Queens valid check

Backtracking Target: 10s

Store queen positions as board[row] = col. Check column clash and diagonal clash (|col_diff| == row_diff).

def is_valid(board, row, col, n):
    for i in range(row):
        if board[i] == col:          return False  # same column
        if abs(board[i]-col) == row-i: return False  # diagonal
    return True

# board[i] = column of queen in row i

Type it from memory. Go.

Practice Problems

• 51. N-Queens
• 52. N-Queens II

Related Coding Drills

• Drill #80 — N-Queens (4x4) Medium
• Drill #21 — Valid parentheses string Easy
• Drill #150 — Valid Parenthesis String Medium