Maximum Subarray Min-Product
<p>The <strong>min-product</strong> of an array is equal to the <strong>minimum value</strong> in the array <strong>multiplied by</strong> the array&#39;s <strong>sum</strong>.</p>

<ul>
	<li>For example, the array <code>[3,2,5]</code> (minimum value is <code>2</code>) has a min-product of <code>2 * (3+2+5) = 2 * 10 = 20</code>.</li>
</ul>

<p>Given an array of integers <code>nums</code>, return <em>the <strong>maximum min-product</strong> of any <strong>non-empty subarray</strong> of </em><code>nums</code>. Since the answer may be large, return it <strong>modulo</strong> <code>10<sup>9</sup> + 7</code>.</p>

<p>Note that the min-product should be maximized <strong>before</strong> performing the modulo operation. Testcases are generated such that the maximum min-product <strong>without</strong> modulo will fit in a <strong>64-bit signed integer</strong>.</p>

<p>A <strong>subarray</strong> is a <strong>contiguous</strong> part of an array.</p>

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

<pre>
<strong>Input:</strong> nums = [1,<u>2,3,2</u>]
<strong>Output:</strong> 14
<strong>Explanation:</strong> The maximum min-product is achieved with the subarray [2,3,2] (minimum value is 2).
2 * (2+3+2) = 2 * 7 = 14.
</pre>

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

<pre>
<strong>Input:</strong> nums = [2,<u>3,3</u>,1,2]
<strong>Output:</strong> 18
<strong>Explanation:</strong> The maximum min-product is achieved with the subarray [3,3] (minimum value is 3).
3 * (3+3) = 3 * 6 = 18.
</pre>

<p><strong class="example">Example 3:</strong></p>

<pre>
<strong>Input:</strong> nums = [3,1,<u>5,6,4</u>,2]
<strong>Output:</strong> 60
<strong>Explanation:</strong> The maximum min-product is achieved with the subarray [5,6,4] (minimum value is 4).
4 * (5+6+4) = 4 * 15 = 60.
</pre>

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

<ul>
	<li><code>1 &lt;= nums.length &lt;= 10<sup>5</sup></code></li>
	<li><code>1 &lt;= nums[i] &lt;= 10<sup>7</sup></code></li>
</ul>
Stack; Array; Prefix Sum; Monotonic Stack
func maxSumMinProduct(nums []int) int {
	n := len(nums)
	left := make([]int, n)
	right := make([]int, n)
	for i := range left {
		left[i] = -1
		right[i] = n
	}
	stk := []int{}
	for i, x := range nums {
		for len(stk) > 0 && nums[stk[len(stk)-1]] >= x {
			stk = stk[:len(stk)-1]
		}
		if len(stk) > 0 {
			left[i] = stk[len(stk)-1]
		}
		stk = append(stk, i)
	}
	stk = []int{}
	for i := n - 1; i >= 0; i-- {
		for len(stk) > 0 && nums[stk[len(stk)-1]] > nums[i] {
			stk = stk[:len(stk)-1]
		}
		if len(stk) > 0 {
			right[i] = stk[len(stk)-1]
		}
		stk = append(stk, i)
	}
	s := make([]int, n+1)
	for i, x := range nums {
		s[i+1] = s[i] + x
	}
	ans := 0
	for i, x := range nums {
		if t := x * (s[right[i]] - s[left[i]+1]); ans < t {
			ans = t
		}
	}
	const mod = 1e9 + 7
	return ans % mod
}