Valid Mountain Array - Array - Easy - LeetCode

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sumitc9127 September 2020Updated: 27 September 2020 1 min read

1A valid mountain array must have at least three elements and follow a specific increasing and then decreasing pattern.
2The function checks if the array first increases to a peak and then decreases, returning true if valid.
3The solution has a time complexity of O(n) and a space complexity of O(1), making it efficient for large arrays.

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"A valid mountain array must have at least three elements and follow a specific increasing and then decreasing pattern."

— Valid Mountain Array - Array - Easy - LeetCode

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

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

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

Example 1:

Input: [2,1] Output: false Example 2:

Input: [3,5,5] Output: false Example 3:

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

Note:

0 <= A.length <= 10000 0 <= A[i] <= 10000

public class Solution {
 public bool ValidMountainArray(int[] A) {
 if(A.Length<3){
 return false;
 }
 
 if(A[0]>A[1]){
 return false;
 }
 
 bool isIncreasing = true; 
 for(int i=1;i<A.Length;i++){
 if(isIncreasing){
 if(A[i-1]>A[i]){
 isIncreasing=false;
 }
 }
 else{
 if(A[i-1]<=A[i]){
 return false;
 }
 }
 }
 
 //check if we found decreasing curve or not
 return isIncreasing==false;
 }
}

Time Complexity: O(n)

Space Complexity: O(1)

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