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40e18905f2
Closes https://github.com/dart-lang/sdk/pull/49478 TEST=Manual GitOrigin-RevId: f4c9c6869dfe73639295e86574a021523b3d374d Change-Id: I134a97caed4eec59d70e9cbca16b7e9a472cf2c1 Reviewed-on: https://dart-review.googlesource.com/c/sdk/+/251902 Reviewed-by: Michael Thomsen <mit@google.com> Commit-Queue: Alexander Thomas <athom@google.com> Reviewed-by: Aske Simon Christensen <askesc@google.com> Reviewed-by: Kevin Chisholm <kevinjchisholm@google.com> Reviewed-by: Alexander Thomas <athom@google.com>
130 lines
3.7 KiB
Dart
130 lines
3.7 KiB
Dart
// Copyright (c) 2011, the Dart project authors. Please see the AUTHORS file
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// for details. All rights reserved. Use of this source code is governed by a
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// BSD-style license that can be found in the LICENSE file.
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// @dart = 2.9
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// Dart test for List.shuffle.
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library shuffle_test;
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import "dart:typed_data";
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import "dart:math" show Random;
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import "package:expect/expect.dart";
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main() {
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for (int size in [0, 1, 2, 3, 7, 15, 99, 1023]) {
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var numbers = new List<int>.generate(size, (x) => x);
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testShuffle(numbers.toList(growable: true));
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testShuffle(numbers.toList(growable: false));
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testShuffle(new Uint32List(size)..setAll(0, numbers));
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testShuffle(new Int32List(size)..setAll(0, numbers));
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testShuffle(new Uint16List(size)..setAll(0, numbers));
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testShuffle(new Int16List(size)..setAll(0, numbers));
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// Some numbers will be truncated in the following two.
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testShuffle(new Uint8List(size)..setAll(0, numbers));
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testShuffle(new Int8List(size)..setAll(0, numbers));
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//testShuffle(numbers.map((x) => "$x").toList());
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}
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// Check that it actually can keep the same list (regression test).
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List l = [1, 2];
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success:
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{
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for (int i = 0; i < 266; i++) {
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int first = l.first;
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l.shuffle();
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if (l.first == first) break success; // List didn't change.
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}
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// Chance of changing 266 times in a row should be < 1:1e80.
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Expect.fail("List changes every time.");
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}
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testRandom();
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}
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void testShuffle(list) {
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List copy = list.toList();
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list.shuffle();
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if (list.length < 2) {
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Expect.listEquals(copy, list);
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return;
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}
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// Test that the list after shuffling has the same elements as before,
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// without considering order.
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Map seen = {};
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for (var e in list) {
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seen[e] = seen.putIfAbsent(e, () => 0) + 1;
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}
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for (var e in copy) {
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int remaining = seen[e];
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remaining -= 1; // Throws if e was not in map at all.
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if (remaining == 0) {
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seen.remove(e);
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} else {
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seen[e] = remaining;
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}
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}
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Expect.isTrue(seen.isEmpty);
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// Test that shuffle actually does make a change. Repeat until the probability
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// of a proper shuffling hitting the same list again is less than 10^80
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// (arbitrary bignum - approx. number of atoms in the universe).
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//
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// The probability of shuffling a list of length n into the same list is
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// 1/n!. If one shuffle didn't change the list, repeat shuffling until
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// probability of randomly hitting the same list every time is less than
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// 1/1e80.
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bool listsDifferent() {
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for (int i = 0; i < list.length; i++) {
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if (list[i] != copy[i]) return true;
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}
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return false;
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}
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if (list.length < 59) {
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// 59! > 1e80.
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double limit = 1e80;
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double fact = 1.0;
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for (int i = 2; i < list.length; i++) fact *= i;
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double combos = fact;
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while (!listsDifferent() && combos < limit) {
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list.shuffle();
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combos *= fact;
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}
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}
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if (!listsDifferent()) {
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Expect.fail("Didn't shuffle at all, p < 1:1e80: $list");
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}
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}
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// Checks that the "random" argument to shuffle is used.
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testRandom() {
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List<int> randomNums = [37, 87, 42, 157, 252, 17];
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List numbers = new List.generate(25, (x) => x);
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List l1 = numbers.toList()..shuffle(new MockRandom(randomNums));
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for (int i = 0; i < 50; i++) {
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// With same random sequence, we get the same shuffling each time.
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List l2 = numbers.toList()..shuffle(new MockRandom(randomNums));
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Expect.listEquals(l1, l2);
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}
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}
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class MockRandom implements Random {
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final List<int> _values;
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int index = 0;
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MockRandom(this._values);
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int get _next {
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int next = _values[index];
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index = (index + 1) % _values.length;
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return next;
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}
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int nextInt(int limit) => _next % limit;
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double nextDouble() => _next / 256.0;
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bool nextBool() => _next.isEven;
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}
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