315

Author: nlfox

315_Count_of_Smaller_Numbers_After_Self.py

@@ -0,0 +1,30 @@
+class BIT(object):
+    def __init__(self, n):
+        self.nums = [0] * (n + 1)
+
+    def update(self, i, v):
+        while i < len(self.nums):
+            self.nums[i] += v
+            i += (i & -i)
+
+    def sum(self, i):
+        s = 0
+        while i > 0:
+            s += self.nums[i]
+            i -= (i & -i)
+        return s
+
+
+class Solution(object):
+    def countSmaller(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[int]
+        """
+        d = {v: i for i, v in enumerate(sorted(set(nums)))}
+        t = BIT(len(nums))
+        res = []
+        for i in xrange(len(nums) - 1, -1, -1):
+            res.append(t.sum(d[nums[i]]))
+            t.update(d[nums[i]] + 1, 1)
+        return res[::-1]