1095. Find in Mountain Array.js

// (This problem is an interactive problem.)
// You may recall that an array A is a mountain array if and only if:
// - A.length >= 3
// - There exists some i with 0 < i < A.length - 1 such that:
//   - A[0] < A[1] < ... A[i-1] < A[i]
//   - A[i] > A[i+1] > ... > A[A.length - 1]
//
// Given a mountain array mountainArr, return the minimum index such that mountainArr.get(index) == target.  If such an index doesn't exist, return -1.
// You can't access the mountain array directly.  You may only access the array using a MountainArray interface:
// - MountainArray.get(k) returns the element of the array at index k (0-indexed).
// - MountainArray.length() returns the length of the array.
//
// Submissions making more than 100 calls to MountainArray.get will be judged Wrong Answer.  Also, any solutions that attempt to circumvent the judge will result in disqualification.
//
// Example 1:
//
// Input: array = [1,2,3,4,5,3,1], target = 3
// Output: 2
// Explanation: 3 exists in the array, at index=2 and index=5. Return the minimum index, which is 2.
//
// Example 2:
//
// Input: array = [0,1,2,4,2,1], target = 3
// Output: -1
// Explanation: 3 does not exist in the array, so we return -1.
//
// Constraints:
//
// 3 <= mountain_arr.length() <= 10000
// 0 <= target <= 10^9
// 0 <= mountain_arr.get(index) <= 10^9

/**
 * // This is the MountainArray's API interface.
 * // You should not implement it, or speculate about its implementation
 * function MountainArray() {
 *
 *     @param {integer} index
 *     @return {integer}
 *     this.get = function(index) {
 *         ...
 *     };
 *
 *     @return {integer}
 *     this.length = function() {
 *         ...
 *     };
 * };
 */
/**
 * @param {number} target
 * @param {MountainArray} mountainArr
 * @return {number}
 */
const findInMountainArray = (target, mountainArr) => {
  const len = mountainArr.length();

  // Find the index of peak
  let peakIdx = 0;
  let l = 0;
  let r = len;
  while (l < r) {
    const m = ~~((l + r) / 2);
    if (mountainArr.get(m) < mountainArr.get(m + 1)) l = peakIdx = m + 1;
    else r = m;
  }

  // Find the target on the left side of peak
  l = 0;
  r = peakIdx - 1;
  while (l <= r) {
    const m = ~~((l + r) / 2);
    if (mountainArr.get(m) === target) return m;
    else if (mountainArr.get(m) < target) l = m + 1;
    else r = m - 1;
  }

  // Find the target on the right side of peak
  l = peakIdx;
  r = len - 1;
  while (l <= r) {
    const m = ~~((l + r) / 2);
    if (mountainArr.get(m) === target) return m;
    else if (mountainArr.get(m) > target) l = m + 1;
    else r = m - 1;
  }
  return -1;
};