我正在尝试查找数组中所有可能元素组合的列表。
例如,让我们考虑一个包含以下元素的数组:' A'' B'' C'' D' ;
如果我选择一个数字作为最大字符串长度,那么我想让所有数组组合达到最大长度。例如:
5 =最大数量;那么:A,AA,AAA,AAAA,AAAAA,AAAAB,AAAAC ....... DDDDD
我做了一个代码。它的速度是可以的,直到最大数量为10.超过15,它开始非常慢。
有人有更好的想法让它更快吗?
这是我的代码:
public static void main(String[] args) {
// TODO Auto-generated method stub
HashSet<String> allResults = new HashSet<String>();
// Create an alphabet to work with
char[] alphabet = new char[] {'A','B','C','D'};
// Find all possible combinations of this alphabet in the string size of 3
StringExcersise.possibleStrings(15, alphabet,"", allResults);
System.out.println(allResults.size());
}
class StringExcersise {
public static void possibleStrings(int maxLength, char[] alphabet, String curr, HashSet<String> allResults) {
// If the current string has reached it's maximum length
if(curr.length() == maxLength) {
allResults.add(curr);
//System.out.println(curr);
// Else add each letter from the alphabet to new strings and process these new strings again
} else {
for(int i = 0; i < alphabet.length; i++) {
String oldCurr = curr;
if(!allResults.contains(oldCurr))
allResults.add(oldCurr);
curr += alphabet[i];
possibleStrings(maxLength,alphabet,curr,allResults);
curr = oldCurr;
}
}
}
}
答案 0 :(得分:2)
结帐Heap's Algorithm
here
Java中的一个工作示例:
private static void swap(int[] v, int i, int j) {
int temp = v[i];
v[i] = v[j];
v[j] = temp;
}
public void permute(int[] v, int n) {
if (n == 1) {
System.out.println(Arrays.toString(v));
} else {
for (int i = 0; i < n; i++) {
permute(v, n-1);
if (n % 2 == 1) {
swap(v, 0, n-1);
} else {
swap(v, i, n-1);
}
}
}
}