From 636e74a76b01a512004b5fc70c5f4445b0fe92d1 Mon Sep 17 00:00:00 2001
From: Elise Pham <elise.pham88@gmail.com>
Date: Fri, 29 Mar 2019 20:03:37 -0700
Subject: [PATCH 1/2] complete matrix_convert_to_zero

---
 lib/matrix_convert_to_zero.rb | 31 ++++++++++++++++++++++++++++---
 1 file changed, 28 insertions(+), 3 deletions(-)

diff --git a/lib/matrix_convert_to_zero.rb b/lib/matrix_convert_to_zero.rb
index 4fb139c..93c93cb 100644
--- a/lib/matrix_convert_to_zero.rb
+++ b/lib/matrix_convert_to_zero.rb
@@ -3,8 +3,33 @@
 # If any number is found to be 0, the method updates all the numbers in the
 # corresponding row as well as the corresponding column to be 0.
 
-# Time complexity: ?
-# Space complexity: ?
+# Time complexity: O(m x n) + O(m + n)
+# Space complexity: O(m + n)
+require "set"
+require "awesome_print"
+
 def matrix_convert_to_zero(matrix)
-  raise NotImplementedError
+  rows = Set.new
+  cols = Set.new
+
+  for i in 0...matrix.length
+    for j in 0...matrix[0].length
+      if matrix[i][j] == 0
+        rows.add(i)
+        cols.add(j)
+      end
+    end
+  end
+
+  rows.each do |r|
+    for c in 0...matrix[0].length
+      matrix[r][c] = 0
+    end
+  end
+
+  cols.each do |c|
+    for r in 0...matrix.length
+      matrix[r][c] = 0
+    end
+  end
 end

From b4afcd2d051b89d9e52606ff95fe335292978136 Mon Sep 17 00:00:00 2001
From: Elise Pham <elise.pham88@gmail.com>
Date: Sat, 30 Mar 2019 23:29:10 -0700
Subject: [PATCH 2/2] More efficient solution no extra space

---
 lib/matrix_convert_to_zero.rb | 39 +++++++++++++++++++++--------------
 1 file changed, 23 insertions(+), 16 deletions(-)

diff --git a/lib/matrix_convert_to_zero.rb b/lib/matrix_convert_to_zero.rb
index 93c93cb..e23ed98 100644
--- a/lib/matrix_convert_to_zero.rb
+++ b/lib/matrix_convert_to_zero.rb
@@ -3,33 +3,40 @@
 # If any number is found to be 0, the method updates all the numbers in the
 # corresponding row as well as the corresponding column to be 0.
 
-# Time complexity: O(m x n) + O(m + n)
-# Space complexity: O(m + n)
-require "set"
+# Time complexity: O(m x n)
+# Space complexity: O(1)
 require "awesome_print"
 
 def matrix_convert_to_zero(matrix)
-  rows = Set.new
-  cols = Set.new
+  column_zero = 1
+  rows = matrix.length
+  cols = matrix[0].length
 
-  for i in 0...matrix.length
-    for j in 0...matrix[0].length
+  for i in 0...rows
+    if matrix[i][0] == 0
+      column_zero = 0
+    end
+
+    for j in 1...cols
       if matrix[i][j] == 0
-        rows.add(i)
-        cols.add(j)
+        matrix[i][0] = matrix[0][j] = 0
       end
     end
   end
 
-  rows.each do |r|
-    for c in 0...matrix[0].length
-      matrix[r][c] = 0
+  i = rows - 1
+  while i >= 0
+    j = cols - 1
+    while j >= 1
+      if matrix[i][0] == 0 || matrix[0][j] == 0
+        matrix[i][j] = 0
+      end
+      j -= 1
     end
-  end
 
-  cols.each do |c|
-    for r in 0...matrix.length
-      matrix[r][c] = 0
+    if column_zero == 0
+      matrix[i][0] = 0
     end
+    i -= 1
   end
 end