Find the peak of an array of central peaks in JavaScript

Center Peak Array

If the following properties are satisfied, we call the array arr Center Peak Array -

• arr.length >= 3

• There are some i and 0

  • arr[0]

  • arr[ i] > arr[i 1] > .. . > arr[arr.length - 1]

Question

We need to write a JavaScript function that accepts a numeric array arr as the first One and only parameter.

The input array is a center peak array. Our function should return the peak index of this central peak array.

For example, if the input to the function is

input

const arr = [4, 6, 8, 12, 15, 11, 7, 4, 1];

output

const output = 4;

Output Explanation

Because the element at index 4 (15) is the peak element of the array.

Example

The following is the code -

Live demonstration

const arr = [4, 6, 8, 12, 15, 11, 7, 4, 1];
const findPeak = (arr = []) => {
   if(arr.length < 3) {
      return -1
   }
   const helper = (low, high) => {
      if(low > high) {
         return -1
      }
      const middle = Math.floor((low + high) / 2)
      if(arr[middle] <= arr[middle + 1]) {
         return helper(middle + 1, high)
      }
      if(arr[middle] <= arr[middle - 1]) {
         return helper(low, middle - 1)
      }
      return middle
   }
   return helper(0, arr.length - 1)
};
console.log(findPeak(arr));

Output

4

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