update

Author: idf

015 Longest Common Prefix.py

@@ -2,8 +2,24 @@
 Write a function to find the longest common prefix string amongst an array of strings.
 """
 __author__ = 'Danyang'
-class Solution:
+
+
+class Solution(object):
     def longestCommonPrefix(self, strs):
+        if not strs: return ""
+        l = min(map(len, strs))
+        i = 0
+        while i < l:
+            char = strs[0][i]
+            for s in strs:
+                if s[i] != char:
+                    return strs[0][:i]
+
+            i += 1
+
+        return strs[0][:i]
+
+    def longestCommonPrefixComplex(self, strs):
         """
         O(k*n)
         :param strs: a list of string
@@ -21,22 +37,21 @@ def longestCommonPrefix(self, strs):
             char = strs[0][i]
 
             j = 0
-            while j<n:
+            while j < n:
                 try:
-                    if strs[j][i]!=char: break
+                    if strs[j][i] != char: break
                     j += 1
                 except IndexError:
                     break
 
-            if j==n:
+            if j == n:
                 str_builder += char
             else:
                 break
 
         return str_builder
 
 
-
-if __name__=="__main__":
+if __name__ == "__main__":
     strs = ["abc", "abcd"]
     print Solution().longestCommonPrefix(strs)

101 Symmetric Tree.py

@@ -20,37 +20,35 @@
 confused what "{1,#,2,3}" means? > read more on how binary tree is serialized on OJ.
 """
 __author__ = 'Danyang'
+
+
 # Definition for a  binary tree node
-class TreeNode:
+class TreeNode(object):
     def __init__(self, x):
         self.val = x
         self.left = None
         self.right = None
 
-class Solution:
+
+class Solution(object):
     def isSymmetric(self, root):
         """
         dfs
         :param root: TreeNode
         :return: boolean
         """
-        # Trivial
         if not root:
             return True
 
         return self.isSymmetrical(root.left, root.right)
 
-
-    def isSymmetrical(self, mirror_left, mirror_right):
-        # Trivial
-        if not mirror_left and not mirror_right:
+    def isSymmetrical(self, l, r):
+        if not l and not r:
             return True
 
         # recursive
-        try:
-            if mirror_left.val==mirror_right.val and self.isSymmetrical(mirror_left.left, mirror_right.right) and self.isSymmetrical(mirror_left.right, mirror_right.left):
-                return True
-        except AttributeError:
-            return False
+        if (l and r and
+            l.val == r.val and self.isSymmetrical(l.left, r.right) and self.isSymmetrical(l.right, r.left)):
+            return True
 
         return False