---
title: "LeetCode #704: Binary Search"
url: https://perrotta.dev/2026/01/leetcode-%23704-binary-search/
last_updated: 2026-01-03
---


[LeetCode #704: Binary Search](https://leetcode.com/problems/binary-search):

From scratch, iteratively:

```python
class Solution:
    def search(self, nums: List[int], target: int) -> int:
        left = 0
        right = len(nums) - 1

        while left <= right:
            ## mid = (left + right) // 2
            mid = left + (right - left) // 2
            assert 0 <= mid < len(nums)

            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                left = mid + 1
            else: ## nums[mid] > target:
                right = mid - 1

        return left if (0 <= left < len(nums)) and nums[left] == target else -1
```

With `bisect`:

```shell
import bisect

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        index = bisect.bisect_left(nums, target)
        if index >= len(nums):
            return -1
        return index if nums[index] == target else -1
```

From scratch, recursively:

```python
import bisect

class Solution:
    def search(self, nums: List[int], target: int) -> int:
        def bsearch(left, right, target):
            ## if not 0 <= left <= right < len(nums):
            ##     return -1
            if left > right:
                return -1

            mid = left + (right - left) // 2

            if nums[mid] == target:
                return mid
            elif nums[mid] < target:
                return bsearch(mid + 1, right, target)
            else:  ## nums[mid] > target
                return bsearch(left, mid - 1, target)

        return bsearch(0, len(nums) - 1, target)
```