Java笛卡爾積演算法原理與實現方法詳解，java笛

Java笛卡爾積演算法原理與實現方法詳解，java笛

本文執行個體講述了Java笛卡爾積演算法原理與實現方法。分享給大家供大家參考，具體如下：

笛卡爾積演算法的Java實現：

（1）迴圈內，每次只有一列向下移一個儲存格，就是CounterIndex指向的那列。
（2）如果該列到尾部了，則這列index重設為0，而CounterIndex則指向前一列，相當於進位，把前列的index加一。
（3）最後，由產生的行數來控制退出迴圈。

public class Test { private static String[] aa = { "aa1", "aa2" }; private static String[] bb = { "bb1", "bb2", "bb3" }; private static String[] cc = { "cc1", "cc2", "cc3", "cc4" }; private static String[][] xyz = { aa, bb, cc }; private static int counterIndex = xyz.length - 1; private static int[] counter = { 0, 0, 0 }; public static void main(String[] args) throws Exception {  for (int i = 0; i < aa.length * bb.length * cc.length; i++) {   System.out.print(aa[counter[0]]);   System.out.print("\t");   System.out.print(bb[counter[1]]);   System.out.print("\t");   System.out.print(cc[counter[2]]);   System.out.println();   handle();  } } public static void handle() {  counter[counterIndex]++;  if (counter[counterIndex] >= xyz[counterIndex].length) {   counter[counterIndex] = 0;   counterIndex--;   if (counterIndex >= 0) {    handle();   }   counterIndex = xyz.length - 1;  } }}

輸出共2*3*4=24行：

aa1 bb1 cc1aa1 bb1 cc2aa1 bb1 cc3aa1 bb1 cc4aa1 bb2 cc1aa1 bb2 cc2aa1 bb2 cc3aa1 bb2 cc4aa1 bb3 cc1aa1 bb3 cc2aa1 bb3 cc3aa1 bb3 cc4aa2 bb1 cc1aa2 bb1 cc2aa2 bb1 cc3aa2 bb1 cc4aa2 bb2 cc1aa2 bb2 cc2aa2 bb2 cc3aa2 bb2 cc4aa2 bb3 cc1aa2 bb3 cc2aa2 bb3 cc3aa2 bb3 cc4

最近碰到了一個笛卡爾積的演算法要求，比如傳遞過來的參數是"1,3,6,7==4,5,8,9==3,4==43,45,8,9==35,4"，則返回的是一個list，如[1,4,3,43,35][1,4,3,43,4][1,4,3,45,35]……，該list包含是4*4*2*4*2=256個元素，現在的思路是這樣的：

import java.util.ArrayList;import java.util.Arrays;import java.util.List;public class DescartesTest { /**  * 擷取N個集合的笛卡爾積  *  * 說明：假如傳入的字串為："1,2,3==5,6==7,8"  *  轉換成字串數組為：[[1, 2, 3], [5, 6], [7, 8]]  *  a=[1, 2, 3]  *  b=[5, 6]  *  c=[7, 8]  *  其大小分別為：a_length=3，b_length=2，c_length=2，  *  目標list的總大小為：totalSize=3*2*2 = 12  *  對每個子集a，b，c，進行迴圈次數=總記錄數/(元素個數*後續集合的笛卡爾積個數)  *  對a中的每個元素迴圈次數=總記錄數/(元素個數*後續集合的笛卡爾積個數)=12/(3*4)=1次，每個元素每次迴圈列印次數：後續集合的笛卡爾積個數=2*2個  *  對b中的每個元素迴圈次數=總記錄數/(元素個數*後續集合的笛卡爾積個數)=12/(2*2)=3次，每個元素每次迴圈列印次數：後續集合的笛卡爾積個數=2個  *  對c中的每個元素迴圈次數=總記錄數/(元素個數*後續集合的笛卡爾積個數)=12/(2*1)=6次，每個元素每次迴圈列印次數：後續集合的笛卡爾積個數=1個  *  *  運行結果：  *  [[1, 2, 3], [5, 6], [7, 8]]   1,5,7,   1,5,8,   1,6,7,   1,6,8,   2,5,7,   2,5,8,   2,6,7,   2,6,8,   3,5,7,   3,5,8,   3,6,7,   3,6,8]   從結果中可以看到：   a中的每個元素每個元素迴圈1次，每次列印4個   b中的每個元素每個元素迴圈3次，每次列印2個   c中的每個元素每個元素迴圈6次，每次列印1個  *  * @param args  */ public static void main(String[] args) {  // TODO Auto-generated method stub  String str ="1,3,6,7==4,5,8,9==3,4==43,45,8,9==35,4";  List<String> result = descartes(str);  System.out.println(result); } @SuppressWarnings("rawtypes") public static List<String> descartes(String str) {  String[] list = str.split("==");  List<List> strs = new ArrayList<List>();  for(int i=0;i<list.length;i++){  strs.add(Arrays.asList(list[i].split(",")));  }  System.out.println(strs);  int total = 1;  for(int i=0;i<strs.size();i++){   total*=strs.get(i).size();  }  String[] mysesult = new String[total];  int now = 1;  //每個元素每次迴圈列印個數  int itemLoopNum = 1;  //每個元素迴圈的總次數  int loopPerItem =1;  for(int i=0;i<strs.size();i++){   List temp = strs.get(i);   now = now*temp.size();   //目標數組的索引值   int index=0;   int currentSize = temp.size();   itemLoopNum = total/now;   loopPerItem = total/(itemLoopNum*currentSize);   int myindex = 0;   for(int j=0;j<temp.size();j++){    //每個元素迴圈的總次數    for(int k=0;k<loopPerItem;k++){     if(myindex==temp.size())      myindex=0;     //每個元素每次迴圈列印個數     for(int m=0;m<itemLoopNum;m++){      mysesult[index]=(mysesult[index]==null?"":mysesult[index]+",")+((String)temp.get(myindex));      index++;     }     myindex++;    }   }  }  return Arrays.asList(mysesult); }}

運行結果輸出：

[[1, 3, 6, 7], [4, 5, 8, 9], [3, 4], [43, 45, 8, 9], [35, 4]]
[1,4,3,43,35, 1,4,3,43,4, 1,4,3,45,35, 1,4,3,45,4, 1,4,3,8,35, 1,4,3,8,4, 1,4,3,9,35, 1,4,3,9,4, 1,4,4,43,35, 1,4,4,43,4, 1,4,4,45,35, 1,4,4,45,4, 1,4,4,8,35, 1,4,4,8,4, 1,4,4,9,35, 1,4,4,9,4, 1,5,3,43,35, 1,5,3,43,4, 1,5,3,45,35, 1,5,3,45,4, 1,5,3,8,35, 1,5,3,8,4, 1,5,3,9,35, 1,5,3,9,4, 1,5,4,43,35, 1,5,4,43,4, 1,5,4,45,35, 1,5,4,45,4, 1,5,4,8,35, 1,5,4,8,4, 1,5,4,9,35, 1,5,4,9,4, 1,8,3,43,35, 1,8,3,43,4, 1,8,3,45,35, 1,8,3,45,4, 1,8,3,8,35, 1,8,3,8,4, 1,8,3,9,35, 1,8,3,9,4, 1,8,4,43,35, 1,8,4,43,4, 1,8,4,45,35, 1,8,4,45,4, 1,8,4,8,35, 1,8,4,8,4, 1,8,4,9,35, 1,8,4,9,4, 1,9,3,43,35, 1,9,3,43,4, 1,9,3,45,35, 1,9,3,45,4, 1,9,3,8,35, 1,9,3,8,4, 1,9,3,9,35, 1,9,3,9,4, 1,9,4,43,35, 1,9,4,43,4, 1,9,4,45,35, 1,9,4,45,4, 1,9,4,8,35, 1,9,4,8,4, 1,9,4,9,35, 1,9,4,9,4, 3,4,3,43,35, 3,4,3,43,4, 3,4,3,45,35, 3,4,3,45,4, 3,4,3,8,35, 3,4,3,8,4, 3,4,3,9,35, 3,4,3,9,4, 3,4,4,43,35, 3,4,4,43,4, 3,4,4,45,35, 3,4,4,45,4, 3,4,4,8,35, 3,4,4,8,4, 3,4,4,9,35, 3,4,4,9,4, 3,5,3,43,35, 3,5,3,43,4, 3,5,3,45,35, 3,5,3,45,4, 3,5,3,8,35, 3,5,3,8,4, 3,5,3,9,35, 3,5,3,9,4, 3,5,4,43,35, 3,5,4,43,4, 3,5,4,45,35, 3,5,4,45,4, 3,5,4,8,35, 3,5,4,8,4, 3,5,4,9,35, 3,5,4,9,4, 3,8,3,43,35, 3,8,3,43,4, 3,8,3,45,35, 3,8,3,45,4, 3,8,3,8,35, 3,8,3,8,4, 3,8,3,9,35, 3,8,3,9,4, 3,8,4,43,35, 3,8,4,43,4, 3,8,4,45,35, 3,8,4,45,4, 3,8,4,8,35, 3,8,4,8,4, 3,8,4,9,35, 3,8,4,9,4, 3,9,3,43,35, 3,9,3,43,4, 3,9,3,45,35, 3,9,3,45,4, 3,9,3,8,35, 3,9,3,8,4, 3,9,3,9,35, 3,9,3,9,4, 3,9,4,43,35, 3,9,4,43,4, 3,9,4,45,35, 3,9,4,45,4, 3,9,4,8,35, 3,9,4,8,4, 3,9,4,9,35, 3,9,4,9,4, 6,4,3,43,35, 6,4,3,43,4, 6,4,3,45,35, 6,4,3,45,4, 6,4,3,8,35, 6,4,3,8,4, 6,4,3,9,35, 6,4,3,9,4, 6,4,4,43,35, 6,4,4,43,4, 6,4,4,45,35, 6,4,4,45,4, 6,4,4,8,35, 6,4,4,8,4, 6,4,4,9,35, 6,4,4,9,4, 6,5,3,43,35, 6,5,3,43,4, 6,5,3,45,35, 6,5,3,45,4, 6,5,3,8,35, 6,5,3,8,4, 6,5,3,9,35, 6,5,3,9,4, 6,5,4,43,35, 6,5,4,43,4, 6,5,4,45,35, 6,5,4,45,4, 6,5,4,8,35, 6,5,4,8,4, 6,5,4,9,35, 6,5,4,9,4, 6,8,3,43,35, 6,8,3,43,4, 6,8,3,45,35, 6,8,3,45,4, 6,8,3,8,35, 6,8,3,8,4, 6,8,3,9,35, 6,8,3,9,4, 6,8,4,43,35, 6,8,4,43,4, 6,8,4,45,35, 6,8,4,45,4, 6,8,4,8,35, 6,8,4,8,4, 6,8,4,9,35, 6,8,4,9,4, 6,9,3,43,35, 6,9,3,43,4, 6,9,3,45,35, 6,9,3,45,4, 6,9,3,8,35, 6,9,3,8,4, 6,9,3,9,35, 6,9,3,9,4, 6,9,4,43,35, 6,9,4,43,4, 6,9,4,45,35, 6,9,4,45,4, 6,9,4,8,35, 6,9,4,8,4, 6,9,4,9,35, 6,9,4,9,4, 7,4,3,43,35, 7,4,3,43,4, 7,4,3,45,35, 7,4,3,45,4, 7,4,3,8,35, 7,4,3,8,4, 7,4,3,9,35, 7,4,3,9,4, 7,4,4,43,35, 7,4,4,43,4, 7,4,4,45,35, 7,4,4,45,4, 7,4,4,8,35, 7,4,4,8,4, 7,4,4,9,35, 7,4,4,9,4, 7,5,3,43,35, 7,5,3,43,4, 7,5,3,45,35, 7,5,3,45,4, 7,5,3,8,35, 7,5,3,8,4, 7,5,3,9,35, 7,5,3,9,4, 7,5,4,43,35, 7,5,4,43,4, 7,5,4,45,35, 7,5,4,45,4, 7,5,4,8,35, 7,5,4,8,4, 7,5,4,9,35, 7,5,4,9,4, 7,8,3,43,35, 7,8,3,43,4, 7,8,3,45,35, 7,8,3,45,4, 7,8,3,8,35, 7,8,3,8,4, 7,8,3,9,35, 7,8,3,9,4, 7,8,4,43,35, 7,8,4,43,4, 7,8,4,45,35, 7,8,4,45,4, 7,8,4,8,35, 7,8,4,8,4, 7,8,4,9,35, 7,8,4,9,4, 7,9,3,43,35, 7,9,3,43,4, 7,9,3,45,35, 7,9,3,45,4, 7,9,3,8,35, 7,9,3,8,4, 7,9,3,9,35, 7,9,3,9,4, 7,9,4,43,35, 7,9,4,43,4, 7,9,4,45,35, 7,9,4,45,4, 7,9,4,8,35, 7,9,4,8,4, 7,9,4,9,35, 7,9,4,9,4]

遞迴演算法：

public static void fn(List<String[]> list,String[] arr,String str){//迭代list List<String> li = new ArrayList<String>();  for(int i=0;i<list.size();i++){   //取得當前的數組   if(i==list.indexOf(arr)){    //迭代數組    System.out.println(arr.length);    for(String st : arr){     st = str + st;     if(i<list.size()-1){      fn(list,list.get(i+1),st);     }else if(i==list.size()-1){      li.add(st);     }    }   }  }  for(int i = 0 ; i < li.size();i++ )  {   System.out.println(li.get(i));  }}