find-rotation-count.js

function findRotationCount(arr, low = 0, high = arr.length - 1) {
    if (high < low) return 0;
    if (high === low) return low;
    let mid = Math.floor((low + high) / 2)
  
    // Check if element (mid+1) is minimum element.
    // Consider the cases like [3, 4, 5, 1, 2]
    if (mid < high && arr[mid + 1] < arr[mid])
      return mid + 1;
  
    // Check if mid itself is minimum element
    if (mid > low && arr[mid] < arr[mid - 1]) {
      return mid;
    }
  
    // Decide whether we need to go to left half or
    // right half
    if (arr[high] > arr[mid]) {
      return findRotationCount(arr, low, mid - 1);
    }
  
    return findRotationCount(arr, mid + 1, high);
  }
  
  module.exports = findRotationCount