907

class Solution {
public:
    int sumSubarrayMins(vector<int>& arr) {
        long ans=0, mod=int(1e9)+7, sz=arr.size();
        stack< pair<int, int> > s1, s2;

        vector<int> left(sz), right(sz);
        for(int i=0; i<sz; i++){
            int count = 1;
            while(!s1.empty() && s1.top().first >= arr[i]){
                count += s1.top().second;
                s1.pop();
            }
            s1.push({arr[i], count});
            left[i] = count;
        }

        for(int i=sz-1; i>=0; i--){
            int count = 1;
            while(!s2.empty() && s2.top().first > arr[i]){
                count += s2.top().second;
                s2.pop();
            }
            s2.push({arr[i], count});
            right[i] = count;
        }

        for(int i=0; i<sz; i++)
            ans = (ans+(long(left[i])*right[i]*arr[i])%mod)%mod;
        return ans;
    }
};