compare version number

Author: Chris Wu

compare-version-numbers.py

@@ -0,0 +1,36 @@
+"""
+i1 and i2 is the pointer we point to the starting point.
+Character before i1 and i2 we already processed.
+When they are set to -1, the whole string are already processed.
+
+#for-loop can't find the '.' any more. [0]
+
+after two version is fully processed and couldn't find which is larger, return 0. [1]
+
+Time Complexity is O(N).
+N is the length of those version, because we potentially loop through them once.
+
+Space Complexity is O(1).
+Because we only store two pointers and two integer.
+"""
+class Solution(object):
+    def compareVersion(self, version1, version2):
+        def getVersion(version, start):
+            if start==-1: return 0, -1
+            for i in xrange(start, len(version)):
+                if version[i]=='.':
+                    return int(version[start:i]), i+1
+            return int(version[start:]), -1 #[0]
+            
+        i1 = i2 = 0
+        
+        while True:
+            sub_version1, i1 = getVersion(version1, i1)
+            sub_version2, i2 = getVersion(version2, i2)
+            
+            if sub_version1>sub_version2:
+                return 1
+            elif sub_version1<sub_version2:
+                return -1
+            elif i1==-1 and i2==-1: #[1]
+                return 0