String database[] = {'a', 'b', 'c'};
我想根据给定的数据库
生成以下字符串序列。
a
b
c
aa
ab
ac
ba
bb
bc
ca
cb
cc
aaa
...
我只能想到一个漂亮的“虚拟”解决方案。
public class JavaApplication21 {
/**
* @param args the command line arguments
*/
public static void main(String[] args) {
char[] database = {'a', 'b', 'c'};
String query = "a";
StringBuilder query_sb = new StringBuilder(query);
for (int a = 0; a < database.length; a++) {
query_sb.setCharAt(0, database[a]);
query = query_sb.toString();
System.out.println(query);
}
query = "aa";
query_sb = new StringBuilder(query);
for (int a = 0; a < database.length; a++) {
query_sb.setCharAt(0, database[a]);
for (int b = 0; b < database.length; b++) {
query_sb.setCharAt(1, database[b]);
query = query_sb.toString();
System.out.println(query);
}
}
query = "aaa";
query_sb = new StringBuilder(query);
for (int a = 0; a < database.length; a++) {
query_sb.setCharAt(0, database[a]);
for (int b = 0; b < database.length; b++) {
query_sb.setCharAt(1, database[b]);
for (int c = 0; c < database.length; c++) {
query_sb.setCharAt(2, database[c]);
query = query_sb.toString();
System.out.println(query);
}
}
}
}
}
解决方案非常愚蠢。从某种意义上说,它是不可扩展的
- 如果我增加
数据库
的大小会怎样? - 如果我的最终目标打印字符串长度需要为 N 怎么办?
是否有任何智能代码,可以以非常智能的方式生成可扩展的排列和组合字符串?
最佳答案
你应该检查这个答案:Getting every possible permutation of a string or combination including repeated characters in Java
获取此代码:
public static String[] getAllLists(String[] elements, int lengthOfList)
{
//lists of length 1 are just the original elements
if(lengthOfList == 1) return elements;
else {
//initialize our returned list with the number of elements calculated above
String[] allLists = new String[(int)Math.pow(elements.length, lengthOfList)];
//the recursion--get all lists of length 3, length 2, all the way up to 1
String[] allSublists = getAllLists(elements, lengthOfList - 1);
//append the sublists to each element
int arrayIndex = 0;
for(int i = 0; i < elements.length; i++){
for(int j = 0; j < allSublists.length; j++){
//add the newly appended combination to the list
allLists[arrayIndex] = elements[i] + allSublists[j];
arrayIndex++;
}
}
return allLists;
}
}
public static void main(String[] args){
String[] database = {"a","b","c"};
for(int i=1; i<=database.length; i++){
String[] result = getAllLists(database, i);
for(int j=0; j<result.length; j++){
System.out.println(result[j]);
}
}
}
虽然可以进一步改进内存,因为这个解决方案首先生成内存(数组)的所有解决方案,然后我们才能打印它。但是思路是一样的,就是用递归算法。
关于java - 生成字符串排列组合的智能方式,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/19993073/