Implement a function that performs binary search on an array of numbers. The function should take in a sorted array of integers and a target integer to find. It returns the index of the target element or -1, if the target element doesn't exist in the array.
binarySearch([1, 2, 3, 6, 9, 11], 6); // 3binarySearch([1, 2, 3, 12, 14, 16], 5); // -1
Binary search is a search algorithm that can efficiently determine if a sorted array of integers contain a specific number. The algorithm repeatedly divides the input array into half until the target element is found, thereby decreasing the search space by half each step. It is a significant improvement versus linear search.
Here is a quick explanation of how binary search works on an array that is already sorted:
Implement a function that performs binary search on an array of numbers. The function should take in a sorted array of integers and a target integer to find. It returns the index of the target element or -1, if the target element doesn't exist in the array.
binarySearch([1, 2, 3, 6, 9, 11], 6); // 3binarySearch([1, 2, 3, 12, 14, 16], 5); // -1
Binary search is a search algorithm that can efficiently determine if a sorted array of integers contain a specific number. The algorithm repeatedly divides the input array into half until the target element is found, thereby decreasing the search space by half each step. It is a significant improvement versus linear search.
Here is a quick explanation of how binary search works on an array that is already sorted:
Binary search is an efficient search algorithm that reduces the search space by half at each step, which means it can find the target element in O(log(n)) time, where n is the size of the input array. This makes it much faster than linear search, which has a time complexity of O(n).
If unspecified:
Note: This question tackles a standard binary search which uses an iterative approach and assumes the array is already sorted. Refer to the 'Notes' section for other alternatives.
/*** @param {Array<number>} arr The input integer array to be searched.* @param {number} target The target integer to search within the array.* @return {number} The index of target element in the array, or -1 if not found.*/export default function binarySearch(arr, target) {// Initialize the left and right indices of the arraylet left = 0;let right = arr.length - 1;// Keep searching until the left and right indices meet.while (left <= right) {// Calculate the mid index to retrieve the mid element later.const mid = Math.floor((left + right) / 2);if (target < arr[mid]) {// If the target element is less than the middle element,// search the left half of the array.// Adjust the right index so the next loop iteration// searches the left side.right = mid - 1;} else if (target > arr[mid]) {// If the target element is greater than the middle element,// search the right half of the array.// Adjust the left index so the next loop iteration// searches the left side.left = mid + 1;} else {// If the target element is equal to the middle element,// return the index of the middle element.return mid;}}// If the element is not found, return -1.return -1;}
If the interviewer asks for a recursive approach:
/*** @param {Array<number>} arr The input integer array to be searched.* @param {number} target Target integer to search within the array* @return {number} Index of target element in the array, or -1 if not found*/export default function binarySearch(arr, target) {return binarySearchImpl(arr, target, 0, arr.length - 1);}function binarySearchImpl(arr, target, left, right) {// Return immediately if the range to search is empty,// since the target element hasn't been found / won't be found.if (left > right) {return -1;}// Calculate the mid index to retrieve the mid element later.const mid = Math.floor((left + right) / 2);if (target < arr[mid]) {// If the target element is less than the middle element,// search the left half of the array and adjust the input// array passed into the recursive call accordingly.return binarySearchImpl(arr, target, left, mid - 1);}if (target > arr[mid]) {// If the target element is greater than the middle element,// search the right half of the array and adjust the input// array passed into the recursive call accordingly.return binarySearchImpl(arr, target, mid + 1, right);}// If the target element is equal to the middle element,// return the index of the middle elementreturn mid;}
Binary search has a time complexity of O(log(n)) in the average and worst case, since it reduces the search space by half every step. Even in the worst scenario where the target element is not within the array, it still reduces the search space by half, hence completing the search within logarithmic time.
In the best case, binary search has a time complexity of O(1). This happens when the target element happens to be at the middle index of the input array.
However, binary search assumes the input array is sorted. If sorting is required, additional time complexity is required depending on the sorting algorithm chosen.
Binary search has a space complexity of O(1) in all cases for the iterative approach, since constant extra memory is used to store variables. We do not reserve additional memory besides the input.
However, if a recursive approach was used, the space complexity depends on the space required for the recursion call stack. Since the height of the recursion tree is log(n) + 1 and there's only 1 recursive call at each level, we expect the space complexity to be O(log(n)).
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