package main

import "fmt"

func numberOfMountainSeen(height []int) int {
	return leftSeen(height) + rightSeen(height)
}

func leftSeen(height []int) int {
	stacks := [][]int{{}}
	res := 0
	for i := 2 ; i < len(height) ; i += 2 {
		preStack := stacks[len(stacks)-1]
		nowStack := append([]int{},preStack...)
		for j := 2 ; j > 0 ; j -- {
			if len(nowStack) == 0 {
				nowStack = append(nowStack, height[i-j])
				continue
			}
			// 当出现大于栈顶元素时，循环比对进行弹栈
			for len(nowStack) > 0 && height[i-j] >= nowStack[len(nowStack)-1] {
				nowStack = nowStack[:len(nowStack)-1]
			}
			nowStack = append(nowStack, height[i-j])
		}
		stacks = append(stacks, nowStack)
		res += len(nowStack)
	}
	return res
}

func rightSeen(height []int) int {
	n := len(height)
	start := (n - 1)- (n % 2)
	stacks := [][]int{{}}
	if n == n - 2 {
		stacks[0] = []int{height[n-1]}
	}
	res := 0
	for i := start - 2  ; i >= 0 ; i -= 2 {
		preStack := stacks[len(stacks)-1]
		nowStack := append([]int{},preStack...)
		for j := 2 ; j > 0 ; j -- {
			if len(nowStack) == 0 {
				nowStack = append(nowStack, height[i+j])
				continue
			}
			// 当出现大于栈顶元素时，循环比对进行弹栈
			for len(nowStack) > 0 && height[i+j] >= nowStack[len(nowStack)-1] {
				nowStack = nowStack[:len(nowStack)-1]
			}
			nowStack = append(nowStack, height[i+j])
		}
		stacks = append(stacks, nowStack)
		res += len(nowStack)
	}
	return res
}


func main() {
	fmt.Println(numberOfMountainSeen([]int{16,5,3,10,21,7}))
}