Today I have done leetcode's July LeetCoding Challenge with cpp.

July LeetCoding Challenge 25

Description

Peak Index in a Mountain Array

An array arr a mountain if the following properties hold:

• arr.length >= 3
• There exists some i with 0 < i < arr.length - 1 such that:
  • arr[0] < arr[1] < ... < arr[i - 1] < arr[i]
  • arr[i] > arr[i + 1] > ... > arr[arr.length - 1]

Given a mountain array arr, return the index i such that arr[0] < arr[1] < ... < arr[i - 1] < arr[i] > arr[i + 1] > ... > arr[arr.length - 1].

You must solve it in O(log(arr.length)) time complexity.

Example 1:

Input: arr = [0,1,0]
Output: 1

Example 2:

Input: arr = [0,2,1,0]
Output: 1

Example 3:

Input: arr = [0,10,5,2]
Output: 1

Constraints:

• 3 <= arr.length <= 105
• 0 <= arr[i] <= 106
• arr is guaranteed to be a mountain array.

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  int peakIndexInMountainArray(vector<int>& arr) {
    int len = arr.size();
    arr.push_back(-1);
    int low = 0;
    int high = len - 1;
    while(low < high) {
      int mid = (low + high) / 2;
      if(arr[mid] < arr[mid + 1]) {
        low = mid + 1;
      } else {
        high = mid;
      }
    }
    return low;
  }
};

// Accepted
// 42/42 cases passed (69 ms)
// Your runtime beats 99.98 % of cpp submissions
// Your memory usage beats 40.39 % of cpp submissions (59.7 MB)