dart - Dart 语言中的笛卡尔积

Question

如何用 Dart 语言创建动态数量列表的笛卡尔积？

例如我有两个列表:X:[A，B，C]； Y:[W，X，Y，Z]

我想创建这样的列表[AW, AX, AY, AZ, BW, BX, BY, BZ, CW, CX, CY, CZ]

虽然Python、Java有预实现的库，但我认为Dart语言没有。

Answer 1

使用 Dart 2.5.0 进行测试:

class PermutationAlgorithmStrings {
  final List<List<String>> elements;

  PermutationAlgorithmStrings(this.elements);

  List<List<String>> permutations() {
    List<List<String>> perms = [];
    generatePermutations(elements, perms, 0, []);
    return perms;
  }

  void generatePermutations(List<List<String>> lists, List<List<String>> result, int depth, List<String> current) {
    if (depth == lists.length) {
      result.add(current);
      return;
    }

    for (int i = 0; i < lists[depth].length; i++) {
      generatePermutations(lists, result, depth + 1, [...current, lists[depth][i]]);
    }
  }
}

您可以输入任意长度的字符串数组。像这样使用:

  PermutationAlgorithmStrings algo = PermutationAlgorithmStrings([
                      ["A", "B", "C"],
                      ["W", "X", "Y", "Z"],
                      ["M", "N"]
                    ]);

输出:

output: [[A, W, M], [A, W, N], [A, X, M], [A, X, N], [A, Y, M], [A, Y, N], [A, Z, M], [A, Z, N], [B, W, M], [B, W, N], [B, X, M], [B, X, N], [B, Y, M], [B, Y, N], [B, Z, M], [B, Z, N], [C, W, M], [C, W, N], [C, X, M], [C, X, N], [C, Y, M], [C, Y, N], [C, Z, M], [C, Z, N]]