message: Update peak-index-in-a-mountain-array.cpp
diff: class Solution {
  public:
  - int peakIndexInMountainArray(vector<int>& A) {
  - int left = 0, right = A.size();
  - while (left < right) {
  + int peakIndexInMountainArray(vector<int>& arr) {
  + int left = 0, right = size(arr) - 1;
  + while (left <= right) {
  const auto mid = left + (right - left) / 2;
  - if (A[mid] > A[mid + 1]) {
  - right = mid;
  + if (arr[mid] > arr[mid + 1]) {
  + right = mid - 1;
  } else {
  left = mid + 1;
  }
  