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lib/model/algorithms.dart

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+
+/// Returns the index in [sortedList] of an element matching the given [key],
+/// if there is one.
+///
+/// Returns -1 if there is no matching element.
+///
+/// The return values of [compare] are interpreted in the same way as for
+/// [Comparable.compareTo]: a negative value of `compare(element, key)` means
+/// the element goes before the key, zero means the element matches the key,
+/// and positive means the element goes after the key.
+///
+/// The list [sortedList] must be sorted in the sense that any elements that
+/// compare before [key] come before any elements that match [key] or
+/// compare after it, and any elements that match [key] come before any
+/// elements that compare after [key].
+/// If the list is not sorted, the return value may be arbitrary.
+///
+/// Only the portion of the list from [start] to [end] (defaulting to 0
+/// and `sortedList.length` respectively, so to the entire list) is searched,
+/// and only that portion need be sorted.
+// Based on binarySearchBy in package:collection/src/algorithms.dart .
+int binarySearchByKey<E, K>(
+  List<E> sortedList,
+  K key,
+  int Function(E element, K key) compare,
+  [int start = 0, int? end]
+) {
+  end = RangeError.checkValidRange(start, end, sortedList.length);
+  int min = start;
+  int max = end;
+  while (min < max) {
+    final mid = min + ((max - min) >> 1);
+    final element = sortedList[mid];
+    final comp = compare(element, key);
+    if (comp == 0) return mid;
+    if (comp < 0) {
+      min = mid + 1;
+    } else {
+      max = mid;
+    }
+  }
+  return -1;
+}