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907. Sum of Subarray Minimums

Given an array of integers A, find the sum of min(B), where B ranges over every (contiguous) subarray of A.

Since the answer may be large, return the answer modulo 10^9 + 7.

 

Example 1:

Input: [3,1,2,4]
Output: 17
Explanation: Subarrays are [3], [1], [2], [4], [3,1], [1,2], [2,4], [3,1,2], [1,2,4], [3,1,2,4]. 
Minimums are 3, 1, 2, 4, 1, 1, 2, 1, 1, 1.  Sum is 17.

 

Note:

  1. 1 <= A.length <= 30000
  2. 1 <= A[i] <= 30000

 

Difficulty:

Medium

Lock:

Normal

Company:

Apple Hulu

Solution(Chinese):

leetcode 907. Sum of Subarray Minimums 解题思路分析