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 <= 104 0 <= arr[i] <= 104
Solution
class Solution { /** * @param Integer[] $arr * @return Boolean */ function validMountainArray($arr) { if( count($arr) < 3 ) return false; if( $arr[0] > $arr[1] ) return false; $peak = array_search(max($arr), $arr); if( $peak == 0 || $peak == (count($arr)-1) ) return false; for( $i = $peak; $i > 1; $i-- ) { if( $arr[$i] <= $arr[$i-1] ) { return false; } } for( $i = $peak; $i < count($arr) - 1; $i++ ) { if( $arr[$i] <= $arr[$i+1] ) { return false; } } return true; } }
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