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I just have tried to solve LeetCode's task 542. 01 Matrix. After a few attempts, I looked for a solution.

rows = len(matrix)
    if rows == 0:
        return []
    
    cols = len(matrix[0])
    
    dis = [[float('inf') for _ in range(cols)] for _ in range(rows)]
    
    q = []
    for i in range(rows):
        for j in range(cols):
            if matrix[i][j] == 0:
                dis[i][j] = 0
                q.append((i, j))
    
    while len(q) > 0:
        x, y = q.pop(0)
        for (a, b) in ((x-1, y), (x+1, y), (x, y-1), (x, y+1)):
            if 0 <= a < rows and 0 <= b < cols and dis[a][b] > dis[x][y] + 1:
                dis[a][b] = dis[x][y] + 1
                q.append((a, b))
    
    return dis

To better understand the code, I changed the line

dis = [[float('inf') for _ in range(cols)] for _ in range(rows)]

to

dis = [[float('inf')]*cols]*rows

After the change, the code test failed. What is the difference between the two?

GreyFox
  • 1
  • Your second list does not contain `rows` sublists. It contains `rows` references to a SINGLE sublist. Change one, you change them all. – Tim Roberts Mar 24 '22 at 22:12

0 Answers0