Live Note

Remain optimistic

6.006 - 1

find the peak.

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/**
 * Find the peek 1D
 * @param {Array<number>} arr arr
 * @param {number} i the index to start
 * @param {number} j the index to end
 * @returns {number} the peak
 */
let findThePeak = (arr, i, j) => {
  let current = parseInt((i + j) / 2)

  if (arr[current] < arr[current + 1]) return findThePeak(arr, current, j)
  else if (arr[current] < arr[current - 1]) return findThePeak(arr, i, current)
  else return arr[current]
}

/**
 * Find the peak 2D
 * @param {Array<Array<number>>} arr the Number[][] array
 * @param {number} start start row
 * @param {number} end end row
 * @returns {number} the peak of the array
 */
let findThePeak2 = (arr, start, end) => {
  let current = parseInt((start + end) / 2)
  let rowMax = findThePeak(arr[current], 0, arr[current].length)

  // get the index of column
  // let i = arr[current].indexOf(rowMax)
  let i = arr[current]
    .map((i, index) => i === rowMax && index)
    .filter((i) => i !== false)[0]

  if (current - 1 >= 0 && arr[current][i] < arr[current - 1][i]) {
    // check the left part
    return findThePeak2(arr, start, current)
  } else if (current < end - 1 && arr[current][i] < arr[current + 1][i]) {
    // check the right part
    return findThePeak2(arr, current, end)
  } else {
    return rowMax
  }
}

let arr = [5, 4, 3, 2, 4, 5, 6]
let arr2 = [
  [6, 3, 8],
  [3, 2, 1],
  [4, 6, 1],
]

console.log(findThePeak(arr, 0, arr.length))
console.log(findThePeak2(arr2, 0, arr2.length))

result:
6 8