Howard的程式筆記

941. Valid Mountain Array (找出陣列中是否有山)

分類於

題目

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

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

Example 2

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

Example 2

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

Constraints:

  • 1 <= arr.length <= 104
  • 0 <= arr[i] <= 104

我的解題

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class Solution {
    public boolean validMountainArray(int[] arr) {
        if(arr.length < 3) return false;
        
        int i = 0;
        
        for(;i<arr.length-1;i++){
            if(arr[i] > arr[i+1]){
                   i++;
                   break;
               }
               else if(arr[i] == arr[i+1]){
                   return false;
               }
        }
        
        if(i < 2) return false;
        
        for(;i<arr.length;i++){
               if(arr[i-1] <= arr[i]){
                   return false;
            }
        }
        return true;
    }
}