From 6fdf1174fb6ee8a091f8767915113eda904d475a Mon Sep 17 00:00:00 2001
From: Azureki <fzureice@gmail.com>
Date: Wed, 22 Aug 2018 16:48:02 +0800
Subject: [PATCH] Sum of Subsequence Widths

---
 lc891.py | 26 ++++++++++++++++++++++++++
 1 file changed, 26 insertions(+)
 create mode 100644 lc891.py

diff --git a/lc891.py b/lc891.py
new file mode 100644
index 0000000..a4a2b64
--- /dev/null
+++ b/lc891.py
@@ -0,0 +1,26 @@
+'''不排序，把所有子数组找出来，然后把极差加起来，这是最麻烦的。
+其次是排序之后二重循环
+O(N)的是等比数列
+'''
+
+class Solution:
+    def sumSubseqWidths(self, A):
+        """
+        :type A: List[int]
+        :rtype: int
+        """
+        A.sort()
+        res=0
+        n=len(A)
+
+        for i in range(n):
+            pos=(1<<i)
+            neg=(1<<(n-1-i))
+            res=(res+(pos-neg)*A[i])%(10**9+7)
+        return res
+
+
+
+A=[2,1,3]
+s=Solution()
+print(s.sumSubseqWidths(A))