10765: ABC140 - E - Second Sum
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Description
Given is a permutation $P$ of $\{1, 2, \ldots, N\}$.
For a pair $(L, R) (1 \le L \lt R \le N)$, let $X_{L, R}$ be the second largest value among $P_L, P_{L+1}, \ldots, P_R$.
Find $\displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}$.
For a pair $(L, R) (1 \le L \lt R \le N)$, let $X_{L, R}$ be the second largest value among $P_L, P_{L+1}, \ldots, P_R$.
Find $\displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}$.
Input
Input is given from Standard Input in the following format:
```
$N$
$P_1$ $P_2$ $\ldots$ $P_N$
```
```
$N$
$P_1$ $P_2$ $\ldots$ $P_N$
```
Output
Print $\displaystyle \sum_{L=1}^{N-1} \sum_{R=L+1}^{N} X_{L,R}$.
Constraints
- $ 2 \le N \le 10^5 $
- $ 1 \le P_i \le N $
- $ P_i \neq P_j $ $(i \neq j)$
- All values in input are integers.
- $ 1 \le P_i \le N $
- $ P_i \neq P_j $ $(i \neq j)$
- All values in input are integers.
Sample 1 Input
3
2 3 1
Sample 1 Output
5
$X_{1, 2} = 2, X_{1, 3} = 2$, and $X_{2, 3} = 1$, so the sum is $2 + 2 + 1 = 5$.
Sample 2 Input
5
1 2 3 4 5
Sample 2 Output
30
Sample 3 Input
8
8 2 7 3 4 5 6 1
Sample 3 Output
136