add python solution

Author: illuz

Diff for: solutions/139.Word_Break/AC_dp_n2.py

@@ -0,0 +1,28 @@
+#!/usr/bin/python
+# -*- coding: utf-8 -*-
+# Author:      illuz <iilluzen[at]gmail.com>
+# File:        AC_dp_n2.py
+# Create Date: 2015-04-21 10:21:18
+# Usage:       AC_dp_n2.py 
+# Descripton:  
+
+
+class Solution:
+    # @param s, a string
+    # @param dict, a set of string
+    # @return a boolean
+    def wordBreak(self, s, dict):
+        n = len(s)
+        dp = [False] * (n + 1)
+        dp[0] = True
+        for i in range(n):
+            if dp[i]:
+                for word in dict:
+                    j = len(word)
+                    if i + j <= n and s[i: i + j] == word:
+                        dp[i + j] = True
+        return dp[n]
+
+# debug
+s = Solution()
+print s.wordBreak('a', ['a'])