| 1 | import 'dart:math'; |
| 2 | |
| 3 | int effectiveValue(int value, int inputCost) => value - inputCost; |
| 4 | |
| 5 | class SelectedCoins { |
| 6 | final List<int> indices; |
| 7 | final bool hasChange; |
| 8 | const SelectedCoins(this.indices, this.hasChange); |
| 9 | } |
| 10 | |
| 11 | SelectedCoins? branchAndBound(List<int> effValues, int target, int costOfChange, |
| 12 | {int maxTries = 100000}) { |
| 13 | final n = effValues.length; |
| 14 | final order = List<int>.generate(n, (i) => i) |
| 15 | ..sort((a, b) => effValues[b].compareTo(effValues[a])); |
| 16 | final sorted = [for (final i in order) effValues[i]]; |
| 17 | final suffix = List<int>.filled(n + 1, 0); |
| 18 | for (var i = n - 1; i >= 0; i--) suffix[i] = suffix[i + 1] + sorted[i]; |
| 19 | final upper = target + costOfChange; |
| 20 | List<int>? best; |
| 21 | final picked = <int>[]; |
| 22 | var tries = 0; |
| 23 | void dfs(int i, int sum) { |
| 24 | if (best != null || tries++ >= maxTries) return; |
| 25 | if (sum > upper) return; |
| 26 | if (sum >= target) { best = List.of(picked); return; } |
| 27 | if (i >= n || sum + suffix[i] < target) return; |
| 28 | picked.add(order[i]); dfs(i + 1, sum + sorted[i]); picked.removeLast(); |
| 29 | dfs(i + 1, sum); |
| 30 | } |
| 31 | dfs(0, 0); |
| 32 | return best == null ? null : SelectedCoins(best!, false); |
| 33 | } |
| 34 | |
| 35 | SelectedCoins? singleRandomDraw(List<int> effValues, int target, int minChange, Random rng) { |
| 36 | final order = List<int>.generate(effValues.length, (i) => i)..shuffle(rng); |
| 37 | final picked = <int>[]; var sum = 0; |
| 38 | for (final i in order) { |
| 39 | picked.add(i); sum += effValues[i]; |
| 40 | if (sum >= target + minChange) return SelectedCoins(picked, true); |
| 41 | } |
| 42 | return null; |
| 43 | } |
| 44 | |
| 45 | /// Branch-and-bound over effective values (value minus the cost of spending the |
| 46 | /// input at the current fee rate). [inputCosts] is parallel to [values] so each |
| 47 | /// input pays for its own script type's size. A match means the excess over |
| 48 | /// [target] stays within [window], so the remainder can be absorbed into the fee |
| 49 | /// instead of creating a change output. Returns null when no such subset exists. |
| 50 | SelectedCoins? changelessMatch({ |
| 51 | required List<int> values, |
| 52 | required int target, |
| 53 | required List<int> inputCosts, |
| 54 | required int window, |
| 55 | int maxTries = 100000, |
| 56 | }) { |
| 57 | assert(values.length == inputCosts.length); |
| 58 | final keep = <int>[]; |
| 59 | final eff = <int>[]; |
| 60 | for (var i = 0; i < values.length; i++) { |
| 61 | final e = effectiveValue(values[i], inputCosts[i]); |
| 62 | if (e > 0) { |
| 63 | keep.add(i); |
| 64 | eff.add(e); |
| 65 | } |
| 66 | } |
| 67 | final match = branchAndBound(eff, target, window, maxTries: maxTries); |
| 68 | if (match == null) return null; |
| 69 | return SelectedCoins([for (final i in match.indices) keep[i]], false); |
| 70 | } |
| 71 | |
| 72 | class InsufficientFundsException implements Exception { const InsufficientFundsException(); } |
| 73 | |
| 74 | SelectedCoins selectCoins({required List<int> values, required int target, |
| 75 | required int inputCost, required int costOfChange, required int minChange, Random? rng}) { |
| 76 | final keep = <int>[]; final eff = <int>[]; |
| 77 | for (var i = 0; i < values.length; i++) { |
| 78 | final e = effectiveValue(values[i], inputCost); |
| 79 | if (e > 0) { keep.add(i); eff.add(e); } |
| 80 | } |
| 81 | SelectedCoins? map(SelectedCoins? s) => |
| 82 | s == null ? null : SelectedCoins([for (final i in s.indices) keep[i]], s.hasChange); |
| 83 | final bnb = map(branchAndBound(eff, target, costOfChange)); |
| 84 | if (bnb != null) return bnb; |
| 85 | final srd = map(singleRandomDraw(eff, target, minChange, rng ?? Random.secure())); |
| 86 | if (srd != null) return srd; |
| 87 | throw const InsufficientFundsException(); |
| 88 | } |