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82 lines
2.0 KiB
Python
82 lines
2.0 KiB
Python
"""
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73. Set Matrix Zeroes
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Difficulty: Medium
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https://leetcode.com/problems/set-matrix-zeroes/
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──────────────────────────────────────────────────
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Given an m x n integer matrix matrix, if an element is 0, set its
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entire row and column to 0's.
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You must do it in place.
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Example 1:
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Input: matrix = [[1,1,1],[1,0,1],[1,1,1]]
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Output: [[1,0,1],[0,0,0],[1,0,1]]
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Example 2:
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Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
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Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]
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Constraints:
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• m == matrix.length
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• n == matrix[0].length
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• 1 <= m, n <= 200
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• -2^31 <= matrix[i][j] <= 2^31 - 1
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Follow up:
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• A straightforward solution using O(mn) space is probably a bad
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idea.
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• A simple improvement uses O(m + n) space, but still not the best
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solution.
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• Could you devise a constant space solution?
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"""
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class Solution:
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def setZeroes(self, matrix: List[List[int]]) -> None:
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"""
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Do not return anything, modify matrix in-place instead.
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"""
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m, n = len(matrix), len(matrix[0])
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# 1. remember if row 0 or column 0 have their own zeros
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row0_zero = any(matrix[0][c] == 0 for c in range(n))
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col0_zero = any(matrix[r][0] == 0 for r in range(m))
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# 2. use row 0 and column 0 as marker lists
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for r in range(1, m):
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for c in range(1, n):
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if matrix[r][c] == 0:
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matrix[r][0] = 0
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matrix[0][c] = 0
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# 3. zero the inner cells from the markers
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for r in range(1, m):
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for c in range(1, n):
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if matrix[r][0] == 0 or matrix[0][c] == 0:
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matrix[r][c] = 0
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# 4. handle row 0 and column 0 last
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if row0_zero:
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for c in range(n):
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matrix[0][c] = 0
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if col0_zero:
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for r in range(m):
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matrix[r][0] = 0
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