Binary Search First Occurrence

Find the first copy of a duplicated target by recording matches and continuing to search the left half.

Algorithm

Basic Implementation

basic.py

arr = [1, 2, 4, 4, 4, 7, 9]
target = 4
lo = 0
hi = len(arr) - 1
result = -1
while lo <= hi:
    mid = lo + (hi - lo) // 2
    if arr[mid] == target:
        result = mid
        hi = mid - 1
    elif arr[mid] < target:
        lo = mid + 1
    else:
        hi = mid - 1
print(result)

Complexity

Time: O(log n)
Space: O(1)

Implementation notes

Keep the explicit control flow. Library shortcuts would hide the state changes this lesson is meant to replay.
The final output is intentionally small and deterministic for cross-language comparison.

execution replay The checked-in replay follows the language-neutral state table for `search-binary-first`.

cross-language comparison This Python DSA version keeps the same data and final output as every other DSA book in this wave.