<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:
    vector<int> prevsmall(vector<int>& arr)
    {   
        stack<int> st;
        vector<int> v;
        for(int i=0;i<arr.size();i++)
        {
            while(!st.empty()&& arr[st.top()]>arr[i])
            {
                st.pop();
            }
            if(st.empty())
            v.push_back(-1);
            else
            v.push_back(st.top());
            st.push(i);
        }
        return v;
    }
    deque<int> nextsmall(vector<int>& arr)
    {   
        stack<int> st;
        deque<int> v;
        for(int i=arr.size()-1;i>=0;i--)
        {
            while(!st.empty()&& arr[st.top()]>=arr[i])
            {
                st.pop();
            }
            if(st.empty())
            v.push_front(arr.size());
            else
            v.push_front(st.top());
            st.push(i);
        }
        return v;
    }
    int sumSubarrayMins(vector<int>& arr) {
        int sum=0;
        vector<int> ps=prevsmall(arr);
        deque<int> ns=nextsmall(arr);
        int mod=1e9+7;
        // for(auto k:ps)
        // {
        //     cout<<k<<endl;
        // }
        // for(auto k:ns)
        // {
        //     cout<<k<<endl;
        // }
        for(int i=0;i<arr.size();i++)
        {
            long long l=i-ps[i];
            long long r=ns[i]-i;
            long long m=(l%mod * r%mod) % mod;
            sum=(sum + (arr[i] * m) % mod) % mod;
        }
        return sum;
    }
};
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