用python解决N Queens problem，给出完整代码（用英语写注释），做成动画显示每一步怎么摆放棋子，以四个棋子为例

Sure, let's solve the N-Queens Problem using Python with an animation to illustrate each step for a four-queens scenario. Here's a complete code snippet with English comments:

import numpy as np
from matplotlib import pyplot as plt
from matplotlib.animation import FuncAnimation

# N-Queens Function
def is_safe(board, row, col):
    # Check if there is no queen in the same column or diagonal
    return not (board[row, :].any() or board[:, col].any() or 
                board[(row + i) % len(board), (col + i)] or 
                board[(row - i) % len(board), (col - i)].any() for i in range(len(board)))

# Generate initial chessboard and solution
def create_board(n):
    board = np.zeros((n, n))
    solutions = []
    return board, solutions

def place_queen(board, n, row=0):
    if row >= n:
        solutions.append(np.copy(board))  # Add solution when all rows filled
        return
    for col in range(n):
        if is_safe(board, row, col):
            board[row, col] = 1
            place_queen(board, n, row + 1)
            board[row, col] = 0  # Backtrack

# Animation function
def animate(solution, frame):
    ax.imshow(solution, cmap='gray', interpolation='nearest')
    ax.set_title(f"Step {frame+1}/{len(solutions)}")
    plt.xticks([], [])
    plt.yticks([], [])

# Initialize plot and data
fig, ax = plt.subplots(figsize=(5, 5))
board, solutions = create_board(4)
solution_index = 0

ani = FuncAnimation(fig, animate, frames=solutions, interval=500, repeat=True)

plt.show()

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