JavaScript Searching and Sorting Algorithm: Find the index of a given element in a sorted array using the binary search algorithm
JavaScript Searching and Sorting Algorithm: Exercise-21 with Solution
Write a JavaScript program to Finds the index of a given element in a sorted array using the binary search algorithm.
- Declare the left and right search boundaries, l and r, initialized to 0 and the length of the array respectively.
- Use a while loop to repeatedly narrow down the search subarray, using Math.floor() to cut it in half.
- Return the index of the element if found, otherwise return -1.
- Note: Does not account for duplicate values in the array.
Sample Solution:
JavaScript Code:
const binarySearch = (arr, item) => {
let l = 0,
r = arr.length - 1;
while (l <= r) {
const mid = Math.floor((l + r) / 2);
const guess = arr[mid];
if (guess === item) return mid;
if (guess > item) r = mid - 1;
else l = mid + 1;
}
return -1;
};
console.log(binarySearch([1, 2, 3, 4, 5], 1));
console.log(binarySearch([1, 2, 3, 4, 5], 5));
console.log(binarySearch([1, 2, 3, 4, 5], 6));
Sample Output:
0 4 -1
Flowchart:
Live Demo:
See the Pen javascript-common-editor by w3resource (@w3resource) on CodePen.
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Previous: Write a JavaScript program to find the lowest index at which a value should be inserted into an array in order to maintain its sorting order, based on the provided iterator function.
Next: Write a JavaScript program to finds the lowest index at which a value should be inserted into an array in order to maintain its sorting order.
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JavaScript: Tips of the Day
How to insert an item into an array at a specific index (JavaScript)?
What you want is the splice function on the native array object.
arr.splice(index, 0, item); will insert item into arr at the specified index (deleting 0 items first, that is, it's just an insert). In this example we will create an array and add an element to it into index 2:
var arr = []; arr[0] = "Jani"; arr[1] = "Hege"; arr[2] = "Stale"; arr[3] = "Kai Jim"; arr[4] = "Borge"; console.log(arr.join()); arr.splice(2, 0, "Lene"); console.log(arr.join());
Ref: https://bit.ly/2BXbp04
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