no message

Author: Chris Wu

README.md

@@ -4,11 +4,9 @@
 2. I really take time tried to make the best solution or explaination. 
 Because I wanted to help others like me. 
 If you like my answer, a star on GitHub means a lot to me. 
-https://github.com/wuduhren/leetcode-python>
+https://github.com/wuduhren/leetcode-python
 
-3. The question is at `https://leetcode.com/problems/the-file-name/`.
-
-	For example, `merge-sorted-array.py`'s question is at `https://leetcode.com/problems/merge-sorted-array/`.
+3. The question is at `https://leetcode.com/problems/the-file-name/`. For example, `merge-sorted-array.py`'s question is at `https://leetcode.com/problems/merge-sorted-array/`.
 
 # Really Great Resources
 ## System Design

add-digits.py

@@ -8,11 +8,4 @@ def addDigits(self, num):
             for d in str(num):
                 total+=int(d)
             num = total
-        return num
-
-"""
-I really take time tried to make the best solution or explaination. 
-Because I wanted to help others like me. 
-If you like my answer, a star on GitHub means a lot to me. 
-https://github.com/wuduhren/leetcode-python
-"""
+        return num

game-of-life.py

@@ -0,0 +1,71 @@
+"""
+As the desscription:
+You cannot update some cells first and then use their updated values to update other cells.
+
+If we wanted to change the state in place,
+We need to set another number that can represent the state now and the next state
+So we don't mess up our count.
+
+So I use 
+3 means alive now and going to die,
+2 means dead now and going alive.
+
+All the '%2' in the count_alive() is just a way to make it cleaner [0]
+Avoiding bunch of if-else
+Because 3%2==1 and 2%2==0
+
+Time Complexity is O(MN)
+Because we go through the whole board once [1]
+Each time at a (i,j) we use O(1) to count its alive neighbor [2]
+And go through the whole board another time to convert 3->0 and 2->1 [3]
+O(MN*1+MN)~=O(MN)
+
+Space Complexity is O(1)
+Because we done it in place.
+
+I learn this really nice and clean solution from @zhuyinghua1203
+"""
+class Solution(object):
+    def gameOfLife(self, board):
+        if board==None or len(board)==0 or len(board[0])==0: return board
+
+        m = len(board)
+        n = len(board[0])
+        
+        def count_alive(i, j):
+            if i<0 or j<0 or i>=m or j>=n: return 0
+            count = 0
+
+            #bottom, top, right, left
+            if i+1<m: count+=board[i+1][j]%2 #[0]
+            if 0<=i-1: count+=board[i-1][j]%2
+            if j+1<n: count+=board[i][j+1]%2
+            if 0<=j-1: count+=board[i][j-1]%2
+
+            #bottomright, topleft, bottomleft, topright
+            if i+1<m and j+1<n: count+=board[i+1][j+1]%2
+            if 0<=i-1 and 0<=j-1: count+=board[i-1][j-1]%2
+            if i+1<m and 0<=j-1: count+=board[i+1][j-1]%2
+            if 0<=i-1 and j+1<n: count+=board[i-1][j+1]%2
+
+            return count
+
+        for i in xrange(m): #[1]
+            for j in xrange(n):
+                count = count_alive(i, j) #[2]
+
+                if board[i][j]==1:
+                    if count<2 or count>3:
+                        board[i][j] = 3
+                elif board[i][j]==0:
+                    if count==3:
+                        board[i][j] = 2
+
+        for i in xrange(m): #[3]
+            for j in xrange(n):
+                if board[i][j]==2:
+                    board[i][j] = 1
+                elif board[i][j]==3:
+                    board[i][j] = 0
+
+        return board