Mbpp/733

def find_first_occurrence(arr, target):
    """
    Returns the index of the first occurrence of target in a sorted array.
    If target is not present, returns -1.
    Uses binary search for O(log n) time complexity.
    """
    left, right = 0, len(arr)
    
    while left < right:
        mid = (left + right) // 2
        if arr[mid] < target:
            left = mid + 1
        else:
            right = mid
            
    # At this point, left is the index of the first element >= target
    if left < len(arr) and arr[left] == target:
        return left
    return -1

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