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

January LeetCoding Challenge 25

Description

Valid Mountain Array

Given an array of integers arr, return true if and only if it is a valid mountain array.

Recall that arr is a mountain array if and only if:

• 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]

Example 1:

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

Example 2:

Input: arr = [3,5,5]
Output: false

Example 3:

Input: arr = [0,3,2,1]
Output: true

Constraints:

• 1 <= arr.length <= 10^4
• 0 <= arr[i] <= 10^4

Solution

auto speedup = [](){
  cin.tie(nullptr);
  cout.tie(nullptr);
  ios::sync_with_stdio(false);
  return 0;
}();
class Solution {
public:
  bool validMountainArray(vector<int>& arr) {
    int len = arr.size();
    if(len < 3) return false;
    int pos = 1;
    if(arr[pos] <= arr[pos - 1]) return false;
    while(pos < len && arr[pos] > arr[pos - 1]) pos += 1;
    if(pos == len || arr[pos] == arr[pos - 1]) return false;
    while(pos < len && arr[pos] < arr[pos - 1]) pos += 1;
    return pos == len;
  }
};

// Accepted
// 53/53 cases passed (16 ms)
// Your runtime beats 99.68 % of cpp submissions
// Your memory usage beats 48.39 % of cpp submissions (22.4 MB)