Find Peak Element Using Binary Search in DSA Typescript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

Output of Peak Element Finder on a Simple Array

What is the output of the following TypeScript code that finds a peak element index in the array?

DSA Typescript

function findPeakElement(nums: number[]): number {
  let left = 0;
  let right = nums.length - 1;
  while (left < right) {
    const mid = Math.floor((left + right) / 2);
    if (nums[mid] > nums[mid + 1]) {
      right = mid;
    } else {
      left = mid + 1;
    }
  }
  return left;
}

const arr = [1, 3, 20, 4, 1, 0];
console.log(findPeakElement(arr));

A 3

B 2

C 1

D 5

💡 Hint

Trace the binary search steps comparing mid and mid+1 elements.

The function uses binary search to find a peak element index. For the array [1, 3, 20, 4, 1, 0], the peak is at index 2 (value 20) because it is greater than its neighbors.

🧠 Conceptual

intermediate

Understanding Peak Element Definition

Which of the following best describes a peak element in an array?

A An element that is smaller than its neighbors.

B An element that is the maximum in the entire array.

C An element that is greater than its immediate neighbors.

D An element that appears more than once in the array.

💡 Hint

Think about local maximums.

A peak element is one that is greater than its neighbors, not necessarily the maximum in the whole array.

🔧 Debug

advanced

Identify the Error in Peak Element Binary Search

What error will the following TypeScript code produce when run?

DSA Typescript

function findPeak(nums: number[]): number {
  let left = 0;
  let right = nums.length - 1;
  while (left <= right) {
    const mid = Math.floor((left + right) / 2);
    if (nums[mid] > nums[mid + 1]) {
      right = mid - 1;
    } else {
      left = mid + 1;
    }
  }
  return left;
}

console.log(findPeak([1, 2, 3, 4]));

A Returns 3

B Returns 2

C Infinite loop

D Runtime error: Index out of bounds

💡 Hint

Check the condition when accessing nums[mid + 1].

The code accesses nums[mid + 1] without checking if mid + 1 is within array bounds, causing a runtime error when mid is the last index.

❓ Predict Output

advanced

Output of Peak Element Finder on Strictly Increasing Array

What is the output of the following TypeScript code when the input array is strictly increasing?

DSA Typescript

function findPeakElement(nums: number[]): number {
  let left = 0;
  let right = nums.length - 1;
  while (left < right) {
    const mid = Math.floor((left + right) / 2);
    if (nums[mid] > nums[mid + 1]) {
      right = mid;
    } else {
      left = mid + 1;
    }
  }
  return left;
}

const arr = [1, 2, 3, 4, 5, 6];
console.log(findPeakElement(arr));

A 5

B 0

C 3

D 6

💡 Hint

In a strictly increasing array, the peak is at the end.

Since the array is strictly increasing, the last element is the peak. The function returns index 5.

🚀 Application

expert

Number of Peak Elements in a Given Array

Given the array [1, 3, 2, 4, 1, 0, 5], how many peak elements does it contain?

A 3

B 2

C 4

D 1

💡 Hint

Count elements greater than neighbors.

Peak elements are at indices 1 (3), 3 (4), and 6 (5). Total 3 peaks.