<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) {
        int n=arr.size();vector<int>res(n);res[0]=arr[0];stack<int>st;st.push(0);int k=1000000007;
        for(int i=1;i<n;i++){
            while((!st.empty())&&(arr[st.top()]>arr[i])){
                st.pop();
            }
            res[i]=(res[i]+(st.empty())?((i+1)*arr[i])%k:((i-st.top())*arr[i])%k)%k;
            if(!st.empty()){
                res[i]=(res[i]+res[st.top()])%k;
            }
            st.push(i);
        }
        int sum=0;
        for(int i=0;i<n;i++){
            sum=(sum+res[i])%k;
        }
        return sum;
    }
};
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