How to Find the Peak in a Bitonic Array Using Binary Search

Code Implementation

The following JavaScript function finds the maximum value in an array that first increases and then decreases (a bitonic array) using a binary‑search‑based approach.

Comment: This problem is essentially a variant of binary search.

function getMaxValue(arr) {
    let len = arr.length;
    // When only one element, return it
    if (len === 1) return arr[0];
    // When the array is strictly decreasing, return first element
    if (arr[0] > arr[1]) return arr[0];
    // When the array is strictly increasing, return last element
    if (arr[len - 1] > arr[len - 2]) return arr[len - 1];
    // Process arrays with both increasing and decreasing parts (at least 3 elements)
    let left = 0,
        right = arr.length - 1;
    while (left < right) {
        let mid = Math.floor((left + right) / 2);
        // Check if arr[mid] is the maximum
        if (mid !== 0 && arr[mid] > arr[mid - 1] && arr[mid] > arr[mid + 1])
            return arr[mid];
        // Determine whether mid is in the increasing part or decreasing part
        if (mid === 0 || arr[mid] > arr[mid - 1]) {
            // increasing part
            left = mid + 1;
        } else if (arr[mid] < arr[mid - 1]) {
            // decreasing part
            right = mid - 1;
        }
    }
    return arr[left];
}