Given an integer array arr, define a subarray's "spread" as its maximum value minus its minimum value. Find the sum of the spreads of every contiguous subarray. Since spread = max − min, the total sum splits cleanly in two: (sum of every subarray's maximum) minus (sum of every subarray's minimum). Each of those two sums is exactly the "sum of subarray minimums" problem — once directly, and once with every comparison flipped to find maximums instead. Each is solved by asking, per element, "in how many subarrays is this element the min (or max)?" — answered with a monotonic stack locating the nearest smaller (or greater) neighbor on each side in a single linear pass. Four linear passes total replace the brute force's quadratic enumeration of every subarray.