solution.ts

function solution(arr: number[]) {
  const longestSubarrays: number[] = []
  let lastElement: number | null = null
  let lastDirection: 'up' | 'down' | null = null
  let currentChainLength: number = 0

  function sum(x: number, agg: number = 0) {
    if (x == 1) {
      return agg + 1
    }

    return sum(x - 1, agg + x)
  }


  for (let x of arr) {
    if (lastElement == null) {
      lastElement = x
      continue
    }

    if (x > lastElement) {
      if (lastDirection == 'down') {
        const i = Math.max(longestSubarrays.length - 1, 0)
        currentChainLength += 1
        longestSubarrays[i] = sum(currentChainLength)
      }

      if (lastDirection == null || lastDirection == 'up') {
        currentChainLength = 1
        longestSubarrays[longestSubarrays.length] = 1
      }

      lastDirection = 'up'
    }

    if (x < lastElement) {
      if (lastDirection == 'up') {
        const i = Math.max(longestSubarrays.length - 1, 0)
        currentChainLength += 1
        longestSubarrays[i] = sum(currentChainLength)
      }

      if (lastDirection == null || lastDirection == 'down') {
        currentChainLength = 1
        longestSubarrays[longestSubarrays.length] = 1
      }

      lastDirection = 'down'
    }

    if (x == lastElement) {
      currentChainLength = 0
      lastDirection = null
    }

    lastElement = x
  }

  return longestSubarrays.reduce((agg, x) => agg + x, 0)
}

console.log(solution([9, 8, 7, 6, 5])) // 4
console.log(solution([2, 3, 7])) // 2
console.log(solution([10, 10, 10])) // 0
console.log(solution([1, 2, 1, 2, 1])) // 10
console.log(
  solution([944846388, 993352669, 473719581, 896064794, 646066085, 7272438041])
) // 15

// [1, 2, 1, 2] // 7
// [1, 2, 1] // 3
// [1, 2] // 1
//
// 1: 1
// 2: 3 // i + (i * i - 1)
// 3: 7 // i + 4
// 4: 10 // i + 6
// 5: 15 // i + 10