Create design-a-leaderboard.py

Author: kamyu104

Python/design-a-leaderboard.py

@@ -0,0 +1,61 @@
+# Time:  ctor:  O(1)
+#        add:   O(1)
+#        top:   O(n)
+#        reset: O(1)
+# Space: O(n)
+
+import collections
+import random
+
+
+class Leaderboard(object):
+
+    def __init__(self):
+        self.__lookup = collections.Counter()
+        
+    def addScore(self, playerId, score):
+        """
+        :type playerId: int
+        :type score: int
+        :rtype: None
+        """
+        self.__lookup[playerId] += score
+
+    def top(self, K):
+        """
+        :type K: int
+        :rtype: int
+        """
+        def kthElement(nums, k, compare):
+            def PartitionAroundPivot(left, right, pivot_idx, nums, compare):
+                new_pivot_idx = left
+                nums[pivot_idx], nums[right] = nums[right], nums[pivot_idx]
+                for i in xrange(left, right):
+                    if compare(nums[i], nums[right]):
+                        nums[i], nums[new_pivot_idx] = nums[new_pivot_idx], nums[i]
+                        new_pivot_idx += 1
+
+                nums[right], nums[new_pivot_idx] = nums[new_pivot_idx], nums[right]
+                return new_pivot_idx
+
+            left, right = 0, len(nums) - 1
+            while left <= right:
+                pivot_idx = random.randint(left, right)
+                new_pivot_idx = PartitionAroundPivot(left, right, pivot_idx, nums, compare)
+                if new_pivot_idx == k:
+                    return
+                elif new_pivot_idx > k:
+                    right = new_pivot_idx - 1
+                else:  # new_pivot_idx < k.
+                    left = new_pivot_idx + 1
+        
+        scores = self.__lookup.values()
+        kthElement(scores, K, lambda a, b: a > b)
+        return sum(scores[:K])
+
+    def reset(self, playerId):
+        """
+        :type playerId: int
+        :rtype: None
+        """
+        self.__lookup[playerId] = 0