Set Matrix Zeroes

0073.Set-Matrix-Zeroes/memo.md

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+# 73. Set Matrix Zeroes
+
+## step1
+空間計算量O(n + m), 時間計算量O(mn)の解法。
+
+> A simple improvement uses O(m + n) space, but still not the best solution.
+> Could you devise a constant space solution?
+
+わからない
+
+## 他の人のコード
+
+https://leetcode.com/problems/set-matrix-zeroes/solutions/6121398/video-o1-space-use-the-first-row-and-col-1kr7/
+
+空間O(1)解法
+
+https://github.com/thonda28/leetcode/pull/9
+
+> 意味のある変数名にしたいです。num_rowsとかでしょうか？
+
+問題文にあわせて m, nにしたがこちらの方がわかりやすいかもしれない
+
+> 0行目と0列目のフラグをそれぞれ用意しなくても、matrix[0][0]をどちらかとみなせますね
+
+読みにくくなると思うので二つフラグを持たせる方針でもよいのでは、と個人的には思う

0073.Set-Matrix-Zeroes/step1.py

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+class Solution:
+    def setZeroes(self, matrix: list[list[int]]) -> None:
+        row_with_zero = set()
+        column_with_zero = set()
+
+        for index_row, row in enumerate(matrix):
+            for index_column, value in enumerate(row):
+                if value == 0:
+                    row_with_zero.add(index_row)
+                    column_with_zero.add(index_column)
+
+        for index_row, row in enumerate(matrix):
+            if index_row in row_with_zero:
+                row[:] = [0] * len(row)
+                continue
+            for index_column in column_with_zero:
+                row[index_column] = 0

0073.Set-Matrix-Zeroes/step1_revised.py

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+class Solution:
+    def setZeroes(self, matrix: list[list[int]]) -> None:
+        row_with_zero = set()
+        column_with_zero = set()
+
+        for r, row in enumerate(matrix):
+            for c, value in enumerate(row):
+                if value == 0:
+                    row_with_zero.add(r)
+                    column_with_zero.add(c)
+
+        for r, row in enumerate(matrix):
+            if r in row_with_zero:
+                row[:] = [0] * len(row)
+                continue
+            for c in column_with_zero:
+                row[c] = 0

0073.Set-Matrix-Zeroes/step2.py

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+class Solution:
+    def setZeroes(self, matrix: list[list[int]]) -> None:
+        if not matrix:
+            return
+
+        m = len(matrix)
+        n = len(matrix[0])
+
+        first_row_has_zero = 0 in matrix[0]
+        first_column_has_zero = any(matrix[r][0] == 0 for r in range(m))
+
+        for r in range(1, m):
+            for c in range(1, n):
+                if matrix[r][c] == 0:
+                    matrix[r][0] = 0
+                    matrix[0][c] = 0
+
+        for r in range(1, m):
+            for c in range(1, n):
+                if matrix[r][0] == 0 or matrix[0][c] == 0:
+                    matrix[r][c] = 0
+
+        if first_row_has_zero:
+            matrix[0] = [0] * n
+
+        if first_column_has_zero:
+            for r in range(m):
+                matrix[r][0] = 0

0073.Set-Matrix-Zeroes/step2_revised.py

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+class Solution:
+    def setZeroes(self, matrix: list[list[int]]) -> None:
+        if not matrix:
+            return
+
+        m = len(matrix)
+        n = len(matrix[0])
+
+        first_row_has_zero = 0 in matrix[0]
+        first_column_has_zero = any(matrix[r][0] == 0 for r in range(m))
+
+        for r in range(1, m):
+            for c in range(1, n):
+                if matrix[r][c] == 0:
+                    matrix[r][0] = 0
+                    matrix[0][c] = 0
+
+        for r in range(1, m):
+            for c in range(1, n):
+                if matrix[r][0] == 0 or matrix[0][c] == 0:
+                    matrix[r][c] = 0
+
+        if first_row_has_zero:
+            matrix[0][:] = [0] * n
+
+        if first_column_has_zero:
+            for r in range(m):
+                matrix[r][0] = 0