Combinations solution

Author: joshguha

77_combinations.py

@@ -0,0 +1,43 @@
+class Solution(object):
+    # def combine(self, n, k):
+    #     """
+    #     :type n: int
+    #     :type k: int
+    #     :rtype: List[List[int]]
+    #     """
+    #     res = []
+    #     candidates = range(1, n + 1)
+    #     self.get_combine(res, candidates, [], k, 0)
+    #     return res
+    #
+    # def get_combine(self, res, candidates, prefix, k, start):
+    #     # recursive
+    #     if k == 0:
+    #         res.append(prefix)
+    #     for index in range(start, len(candidates)):
+    #         self.get_combine(res, candidates,
+    #                          prefix + [candidates[index]],
+    #                          k - 1, index + 1)
+
+    def combine(self, n, k):
+        res = []
+        self.get_combine(res, [], n, k, 1)
+        return res
+
+    def get_combine(self, res, prefix, n, k, start):
+        # recursive with only one array
+        if k == 0:
+            res.append(list(prefix))
+        elif start <= n:
+            prefix.append(start)
+            self.get_combine(res, prefix,
+                             n, k - 1, start + 1)
+            prefix.pop()
+            self.get_combine(res, prefix,
+                             n, k, start + 1)
+
+
+
+if __name__ == "__main__":
+    s = Solution()
+    print s.combine(4, 2)