题目地址：

https://leetcode.com/problems/sum-of-subarray-ranges/

给定一个长$n$数组$A$，求${\sum }_{l\le r}(\max A[l:r]-\min A[l:r])$。

参考https://blog.csdn.net/qq_46105170/article/details/109734115。代码如下：

class Solution {
    
 public:
  using LL = long long;

  LL subArrayRanges(vector<int>& nums) {
    
    auto less = [](int& x, int& y) {
     return x <= y; };
    auto more = [](int& x, int& y) {
     return x >= y; };
    return calc(nums, more) - calc(nums, less);
  }

  LL calc(vector<int>& v, bool (*comp)(int&, int&)) {
    
    stack<int> stk;
    LL res = 0;
    for (int i = 0; i < v.size(); i++) {
    
      while (stk.size() && comp(v[i], v[stk.top()])) {
    
        int idx = stk.top(); stk.pop();
        int l = idx - (stk.size() ? stk.top() : -1), r = i - idx;
        res += (LL)v[idx] * l * r;
      }
      stk.push(i);
    }

    while (stk.size()) {
    
      int idx = stk.top(); stk.pop();
      int l = idx - (stk.size() ? stk.top() : -1), r = v.size() - idx;
      res += (LL)v[idx] * l * r;
    }

    return res;
  }
};

时空复杂度$O(n)$。