You are given an array of positive integers nums.
Return the number of subarrays of nums, where the first and the last elements of the subarray are equal to the largest element in the subarray.
\n
Example 1:
\n\nInput: nums = [1,4,3,3,2]
\n\nOutput: 6
\n\nExplanation:
\n\nThere are 6 subarrays which have the first and the last elements equal to the largest element of the subarray:
\n\n[1,4,3,3,2], with its largest element 1. The first element is 1 and the last element is also 1.[1,4,3,3,2], with its largest element 4. The first element is 4 and the last element is also 4.[1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3.[1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3.[1,4,3,3,2], with its largest element 2. The first element is 2 and the last element is also 2.[1,4,3,3,2], with its largest element 3. The first element is 3 and the last element is also 3.Hence, we return 6.
\nExample 2:
\n\nInput: nums = [3,3,3]
\n\nOutput: 6
\n\nExplanation:
\n\nThere are 6 subarrays which have the first and the last elements equal to the largest element of the subarray:
\n\n[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.[3,3,3], with its largest element 3. The first element is 3 and the last element is also 3.Hence, we return 6.
\nExample 3:
\n\nInput: nums = [1]
\n\nOutput: 1
\n\nExplanation:
\n\nThere is a single subarray of nums which is [1], with its largest element 1. The first element is 1 and the last element is also 1.
Hence, we return 1.
\n\n
Constraints:
\n\n1 <= nums.length <= 1051 <= nums[i] <= 109给你一个 正 整数数组 nums 。
请你求出 nums 中有多少个子数组，满足子数组中 第一个 和 最后一个 元素都是这个子数组中的 最大 值。
\n\n
示例 1：
\n\n输入：nums = [1,4,3,3,2]
\n\n输出：6
\n\n解释：
\n\n总共有 6 个子数组满足第一个元素和最后一个元素都是子数组中的最大值：
\n\n[1,4,3,3,2] ，最大元素为 1 ，第一个和最后一个元素都是 1 。[1,4,3,3,2] ，最大元素为 4 ，第一个和最后一个元素都是 4 。[1,4,3,3,2] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[1,4,3,3,2] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[1,4,3,3,2] ，最大元素为 2 ，第一个和最后一个元素都是 2 。[1,4,3,3,2] ，最大元素为 3 ，第一个和最后一个元素都是 3 。所以我们返回 6 。
\n示例 2：
\n\n输入：nums = [3,3,3]
\n\n输出：6
\n\n解释：
\n\n总共有 6 个子数组满足第一个元素和最后一个元素都是子数组中的最大值：
\n\n[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。[3,3,3] ，最大元素为 3 ，第一个和最后一个元素都是 3 。所以我们返回 6 。
\n示例 3：
\n\n输入：nums = [1]
\n\n输出：1
\n\n解释：
\n\nnums 中只有一个子数组 [1] ，最大元素为 1 ，第一个和最后一个元素都是 1 。
所以我们返回 1 。
\n\n\n
提示：
\n\n1 <= nums.length <= 1051 <= nums[i] <= 109nums[i], we can count the number of valid subarrays ending with it.",
"For each index i, find the nearest index j on its left (j < i) such that nums[j] < nums[i]. This can be done via a monotonic stack.",
"For each index i, find the number of indices k in the window [j + 1, i] such that nums[k] == nums[i], this is the number of the valid subarrays ending with nums[i]. This can be done by sliding window.",
"Sum the answer of all the indices i to get the final result.",
"Is it possible to use DSU as an alternate solution?"
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