Java基于递归和循环两种方式实现未知维度集合的笛卡尔积算法示例

import java.util.ArrayList;
import java.util.Arrays;
import java.util.List;
/**
 * 循环和递归两种方式实现未知维度集合的笛卡尔积
 * Created on 2015-05-22
 * @author luweijie
 */
public class Descartes {
  /**
   * 递归实现dimValue中的笛卡尔积，结果放在result中
   * @param dimValue 原始数据
   * @param result 结果数据
   * @param layer dimValue的层数
   * @param curList 每次笛卡尔积的结果
   */
  private static void recursive (List<List<String>> dimValue, List<List<String>> result, int layer, List<String> curList) {
    if (layer < dimValue.size() - 1) {
      if (dimValue.get(layer).size() == 0) {
        recursive(dimValue, result, layer + 1, curList);
      } else {
        for (int i = 0; i < dimValue.get(layer).size(); i++) {
          List<String> list = new ArrayList<String>(curList);
          list.add(dimValue.get(layer).get(i));
          recursive(dimValue, result, layer + 1, list);
        }
      }
    } else if (layer == dimValue.size() - 1) {
      if (dimValue.get(layer).size() == 0) {
        result.add(curList);
      } else {
        for (int i = 0; i < dimValue.get(layer).size(); i++) {
          List<String> list = new ArrayList<String>(curList);
          list.add(dimValue.get(layer).get(i));
          result.add(list);
        }
      }
    }
  }
  /**
   * 循环实现dimValue中的笛卡尔积，结果放在result中
   * @param dimValue 原始数据
   * @param result 结果数据
   */
  private static void circulate (List<List<String>> dimValue, List<List<String>> result) {
    int total = 1;
    for (List<String> list : dimValue) {
      total *= list.size();
    }
    String[] myResult = new String[total];
    int itemLoopNum = 1;
    int loopPerItem = 1;
    int now = 1;
    for (List<String> list : dimValue) {
      now *= list.size();
      int index = 0;
      int currentSize = list.size();
      itemLoopNum = total / now;
      loopPerItem = total / (itemLoopNum * currentSize);
      int myIndex = 0;
      for (String string : list) {
        for (int i = 0; i < loopPerItem; i++) {
          if (myIndex == list.size()) {
            myIndex = 0;
          }
          for (int j = 0; j < itemLoopNum; j++) {
            myResult[index] = (myResult[index] == null? "" : myResult[index] + ",") + list.get(myIndex);
            index++;
          }
          myIndex++;
        }
      }
    }
    List<String> stringResult = Arrays.asList(myResult);
    for (String string : stringResult) {
      String[] stringArray = string.split(",");
      result.add(Arrays.asList(stringArray));
    }
  }
  /**
   * 程序入口
   * @param args
   */
  public static void main (String[] args) {
    List<String> list1 = new ArrayList<String>();
    list1.add("1");
    list1.add("2");
    List<String> list2 = new ArrayList<String>();
    list2.add("a");
    list2.add("b");
    List<String> list3 = new ArrayList<String>();
    list3.add("3");
    list3.add("4");
    list3.add("5");
    List<String> list4 = new ArrayList<String>();
    list4.add("c");
    list4.add("d");
    list4.add("e");
    List<List<String>> dimValue = new ArrayList<List<String>>();
    dimValue.add(list1);
    dimValue.add(list2);
    dimValue.add(list3);
    dimValue.add(list4);
    List<List<String>> recursiveResult = new ArrayList<List<String>>();
    // 递归实现笛卡尔积
    recursive(dimValue, recursiveResult, 0, new ArrayList<String>());
    System.out.println("递归实现笛卡尔乘积: 共 " + recursiveResult.size() + " 个结果");
    for (List<String> list : recursiveResult) {
      for (String string : list) {
        System.out.print(string + " ");
      }
      System.out.println();
    }
    List<List<String>> circulateResult = new ArrayList<List<String>>();
    circulate(dimValue, circulateResult);
    System.out.println("循环实现笛卡尔乘积: 共 " + circulateResult.size() + " 个结果");
    for (List<String> list : circulateResult) {
      for (String string : list) {
        System.out.print(string + " ");
      }
      System.out.println();
    }
  }
}

递归实现笛卡尔乘积: 共 36 个结果
1 a 3 c
1 a 3 d
1 a 3 e
1 a 4 c
1 a 4 d
1 a 4 e
1 a 5 c
1 a 5 d
1 a 5 e
1 b 3 c
1 b 3 d
1 b 3 e
1 b 4 c
1 b 4 d
1 b 4 e
1 b 5 c
1 b 5 d
1 b 5 e
2 a 3 c
2 a 3 d
2 a 3 e
2 a 4 c
2 a 4 d
2 a 4 e
2 a 5 c
2 a 5 d
2 a 5 e
2 b 3 c
2 b 3 d
2 b 3 e
2 b 4 c
2 b 4 d
2 b 4 e
2 b 5 c
2 b 5 d
2 b 5 e
循环实现笛卡尔乘积: 共 36 个结果
1 a 3 c
1 a 3 d
1 a 3 e
1 a 4 c
1 a 4 d
1 a 4 e
1 a 5 c
1 a 5 d
1 a 5 e
1 b 3 c
1 b 3 d
1 b 3 e
1 b 4 c
1 b 4 d
1 b 4 e
1 b 5 c
1 b 5 d
1 b 5 e
2 a 3 c
2 a 3 d
2 a 3 e
2 a 4 c
2 a 4 d
2 a 4 e
2 a 5 c
2 a 5 d
2 a 5 e
2 b 3 c
2 b 3 d
2 b 3 e
2 b 4 c
2 b 4 d
2 b 4 e
2 b 5 c
2 b 5 d
2 b 5 e