<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> pseef(vector<int>& nums){
            stack<int> st;
            vector<int> ans;
            int n=nums.size();
            for(int i=0;i<n;i++){
                while (!st.empty() && nums[st.top()]>nums[i]){
                    st.pop();
                }
                if (st.empty()){
                    ans.push_back(-1);
                }
                else{
                    ans.push_back(st.top());
                }
                st.push(i);
            }
            return ans;
        }
    vector<int> nsef(vector<int>& nums){
            stack<int> st;
            int n=nums.size();
            vector<int> ans(n,0);
            for(int i=n-1;i>=0;i--){
                while (!st.empty() && nums[st.top()]>=nums[i]){
                    st.pop();
                }
                if (st.empty()){
                    ans[i]=n;
                }
                else{
                    ans[i]=st.top();
                }
                st.push(i);
            }
            return ans;
        }

    int sumSubarrayMins(vector<int>& arr) {
        long long int ans=0;
        int n=arr.size();
        const int MOD=1e9+7;
        vector<int> psee=pseef(arr);
        vector<int> nse=nsef(arr);
        for(int i=0;i<n;i++){
            ans+=static_cast<long long>(i-psee[i])*(nse[i]-i)*arr[i]%MOD;
            ans=ans%MOD;
        }
        return ans;
    }
};
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