Leetcode

852. Peak Index in a Mountain Array

by hooni posted Apr 28, 2020
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Let's call an array A a mountain if the following properties hold:

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

Given an array that is definitely a mountain, return any i such that A[0] < A[1] < ... A[i-1] < A[i] > A[i+1] > ... > A[A.length - 1].

Example 1:

Input: [0,1,0]
Output: 1

Example 2:

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

Note:

  1. 3 <= A.length <= 10000
  2. 0 <= A[i] <= 10^6
  3. A is a mountain, as defined above.


/*
//가장 높은 점이 몇개인지 찾으라고 잘못 이해하고 만든..
class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int max = -1;
        Map<Integer, Integer> hmap = new HashMap<>();
        
        for(int i=0; i<A.length; i++){
            if(max < A[i]){
                max = A[i];
                hmap.put(max, hmap.getOrDefault(A[i],0)+1);
            }
        }
        
        return hmap.get(max);
    }
}
*/
//가장 높은 곳까지 올라가는 횟수
class Solution {
    public int peakIndexInMountainArray(int[] A) {
        int count = 0;
        for(int i=0; i<A.length-1; i++){
            if(A[i] < A[i+1]){
                count++;
            }
        }
        
        return count;
    }
}


[문제] https://leetcode.com/problems/peak-index-in-a-mountain-array/