<p>Given an array of integers arr, find the sum of <code>min(b)</code>, where <code>b</code> ranges over every (contiguous) subarray of <code>arr</code>. Since the answer may be large, return the answer <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

<p>&nbsp;</p>
<p><strong class="example">Example 1:</strong></p>

<pre>
<strong>Input:</strong> arr = [3,1,2,4]
<strong>Output:</strong> 17
<strong>Explanation:</strong> 
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.
</pre>

<p><strong class="example">Example 2:</strong></p>

<pre>
<strong>Input:</strong> arr = [11,81,94,43,3]
<strong>Output:</strong> 444
</pre>

<p>&nbsp;</p>
<p><strong>Constraints:</strong></p>

<ul>
	<li><code>1 &lt;= arr.length &lt;= 3 * 10<sup>4</sup></code></li>
	<li><code>1 &lt;= arr[i] &lt;= 3 * 10<sup>4</sup></code></li>
</ul>

class Solution {
public:
    int sumSubarrayMins(vector<int>& arr) {
        stack<pair<int, int>> s;
        long long n=arr.size(), mod=1e9 +7, ans=0;
        for(int i=0; i<n; i++){
            while(!s.empty() && s.top().first>arr[i]){
                pair<int,int> temp=s.top();
                s.pop();
                long long left=temp.second+1-(s.empty()?0:(s.top().second+1)), right=i-temp.second;
                ans = (ans+((right*left*temp.first)%mod))%mod;
            }
            s.push({arr[i], i});
        }
        while(!s.empty()){
            pair<int,int> temp=s.top();
            s.pop();
            long long left=temp.second+1-(s.empty()?0:(s.top().second+1)), right=n-temp.second;
            ans = (ans+((right*left*temp.first)%mod))%mod;
        }
        return ans;
    }
};
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