java-输入一个字符串，输出该字符串中字符的所有组合。举个例子，如果输入abc，它的组合有a、b、c、ab、ac、bc、abc

import java.util.ArrayList;
import java.util.List;

public class Combination {

	public static void main(String[] args) {

		char[] a = { 'a', 'b', 'c' };
		List<Character> list = new ArrayList<Character>();
		for (int i = 1, len = a.length; i <= len; i++) {
			combine(a, 0, i, list);
		}
	}
        /*
	 * we can also use Stack like this:
	    stack.push(a[begin]);
		combination(a,begin+1,number-1,stack);
		stack.pop();
		combination(a,begin+1,number,stack);
	 */
	public static void combine(char[] a, int begin, int resultLength,List<Character> list) {
		
		if (resultLength == 0) {
			System.out.println(list.toString());
			return;
		}
		if (begin == a.length){
			return;
		}
		
		list.add(a[begin]);
		combine(a, begin + 1, resultLength - 1, list);
		list.remove((Character) a[begin]);
		combine(a, begin + 1, resultLength, list);
	}
}

the idea is fromhttp://zhedahht.blog.163.com/blog/static/2541117420114172812217/