941. Valid Mountain Array

Problem

Tags: 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

Code

C

// 941. Valid Mountain Array (7/13/54000)
// Runtime: 40 ms (30.08%) Memory: 6.94 MB (61.02%) 



bool validMountainArray(int arr[], int arrSize){
    if (arrSize < 3) {
        return false;
    }
    
    if (arr[1] < arr[0]) {
        return false;
    }
    
    size_t i = 1;
    while (i < arrSize - 1 && arr[i] > arr[i - 1]) {
        i++;
    }
    while (i < arrSize && arr[i] < arr[i - 1]) {
        i++;
    }
    
    return i == arrSize;
}