35 lines
1004 B
Markdown
35 lines
1004 B
Markdown
---
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title: binarySearch
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tags: algorithm,array,beginner
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firstSeen: 2020-12-28T12:35:44+02:00
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lastUpdated: 2020-12-29T13:06:47+02:00
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---
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Finds the index of a given element in a sorted array using the binary search algorithm.
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- Declare the left and right search boundaries, `l` and `r`, initialized to `0` and the `length` of the array respectively.
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- Use a `while` loop to repeatedly narrow down the search subarray, using `Math.floor()` to cut it in half.
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- Return the index of the element if found, otherwise return `-1`.
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- **Note:** Does not account for duplicate values in the array.
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```js
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const binarySearch = (arr, item) => {
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let l = 0,
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r = arr.length - 1;
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while (l <= r) {
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const mid = Math.floor((l + r) / 2);
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const guess = arr[mid];
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if (guess === item) return mid;
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if (guess > item) r = mid - 1;
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else l = mid + 1;
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}
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return -1;
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};
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```
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```js
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binarySearch([1, 2, 3, 4, 5], 1); // 0
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binarySearch([1, 2, 3, 4, 5], 5); // 4
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binarySearch([1, 2, 3, 4, 5], 6); // -1
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```
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