<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> findNSE(vector<int> &arr) {
        vector<int> nse(arr.size());
        stack<int> st;
        for(int i = arr.size() - 1; i >= 0;i--) {
            while(!st.empty() && arr[st.top()] >= arr[i]) {
                st.pop();
            }
            nse[i] = st.empty() ? arr.size() : st.top();
            st.push(i);
        }
        return nse;
    }
    vector<int> findPSEE(vector<int> &arr) {
        vector<int> pse(arr.size());
        stack<int> st;
        for(int i = 0; i < arr.size(); i++) {
            while(!st.empty() && arr[st.top()] > arr[i]) {
                st.pop();
            }
            pse[i] = st.empty() ? -1 : st.top();
            st.push(i);
        }
        return pse;
    }
    int sumSubarrayMins(vector<int>& arr) {
        long long total = 0, mod = 1e9 +7;
        vector<int> nse = findNSE(arr);
        vector<int> psee = findPSEE(arr);
        for(int i = 0; i < arr.size(); i++) {
            long long left = i - psee[i];
            long long right = nse[i] - i;
            total = (total + (left*right*arr[i]) % mod) % mod;
        }
        return total;
    }
};
45800