Merge pull request SocialfiPanda#5 from yjc801/patch-1

merge word break II alternate solution

Author: SocialfiPanda

Word Break II.py

@@ -1,28 +1,26 @@
-class Solution:  
-    def canBreak(self, s, dict):
-        possible = []
-        for i in range(len(s)):
-            if s[:i + 1] in dict:
-                possible.append(True)
-            else:
-                found = False
-                for j in range(i):
-                    if possible[j] == True and s[j + 1: i + 1] in dict:
-                        found = True
-                        break
-                possible.append(found)
-        return possible[len(s) - 1]
-        
+class Solution:
     def wordBreak(self, s, dict):
-        result = {}
-        if not self.canBreak(s, dict):
-            return []
-        for i in range(len(s)):
-            result[s[:i + 1]] = []
-            if s[:i + 1] in dict:
-                result[s[:i + 1]] = [s[:i + 1]]
-            for j in range(i):
-                if s[:j + 1] in result and s[j + 1: i + 1] in dict:
-                    for k in result[s[:j + 1]]:
-                        result[s[:i + 1]].append(k + " " + s[j + 1: i + 1])
-        return result[s]
+        n = len(s)
+        f = [False for _ in xrange(n)]
+        trace = [[False] * n for _ in xrange(n)]
+        for i in xrange(n):
+            trace.append([])
+            if s[:i+1] in dict:
+                f[i] = True
+                trace[0][i] = True
+            for j in xrange(i):
+                if f[j] and s[j+1:i+1] in dict:
+                    f[i] = True
+                    trace[j+1][i] = True
+        result = []
+        if f[n-1]:
+            self.backtrack(s, trace, 0, [], result)
+        return result
+    
+    def backtrack(self, s, trace, start, path, result):
+        if start == len(s):
+            result.append(" ".join(path))
+            return
+        for i in xrange(start, len(s)):
+            if trace[start][i]:
+                self.backtrack(s, trace, i + 1, path + [s[start:i+1]], result)