Added alternative solution

Author: shichao-an

permutations_ii/solution2.py

@@ -0,0 +1,21 @@
+class Solution:
+    # @param num, a list of integer
+    # @return a list of lists of integers
+    def permuteUnique(self, num):
+        return self.permute(sorted(num))
+
+    def permute(self, num):
+        if not num:
+            return [[]]
+        else:
+            res = []
+            prev = None
+            for i, e in enumerate(num):
+                if prev is None or prev != e:
+                    rest = num[:i] + num[i + 1:]
+                    rest_perms = self.permute(rest)
+                    for perm in rest_perms:
+                        perm.append(e)
+                    res += rest_perms
+                    prev = e
+            return res