GLOBAL TEMPLATE: "Find first true"

binary_search.py

from collections.abc import Callable

def binary_search(array: list[int], condition: Callable[[int], bool]) -> int:
    left, right = 0, len(array)  # insertion point may be after last element
    # half-open interval [left, right) so no candidates when left === right
    while left < right:
        mid = (left + right) // 2

        if condition(mid):  # monotonic condition
            right = mid  # mid might still be the first true
        else:
            left = mid + 1

    # if not found, inserting at left maintains sorted order
    return left

binarySearch.ts

const binarySearch = (length: number, condition: (idx: number) => boolean): number => {
  let [left, right] = [0, length]; // insertion point may be after the last element
  // half-open interval [left, right) so no candidates when left === right
  while (left < right) {
    const mid = Math.floor((left + right) / 2);

    if (condition(mid)) { // monotonic condition
      right = mid; // mid might still be the first true
    } else {
      left = mid + 1;
    }
  }

  // if not found, inserting `target` at `left` maintains order
  return left;
};