如何修改代码让最后文字搜寻游戏中的单词不重叠覆盖

Question

1. Wordsearch Puzzle是一个单词搜寻游戏让用户输入单词并得到一个字母矩阵的输出但是最后的输出会出现字母重叠请客

def add(word, puzzle):
method = random.randint(0, 2)
if method == 0:
row = random.randint(0, 20)
column = random.randint(0, 20-len(word))
for i in range(0, len(word)):
puzzle[row][column+i] = word[i]
elif method == 1:
column = random.randint(0, 20)
row = random.randint(0, 20-len(word))
for i in range(0, len(word)):
puzzle[row+i][column] = word[i]
else:
row = random.randint(0, 20-len(word))
for i in range(0, len(word)):
puzzle[row+i][row+i+1] = word[i]

如何让最后放在表格里的单词不重叠覆盖求教