排列遞歸

遞歸算法:

/**
	 * 求排列(遞歸)
	 * @param result 最終排列結果
	 * @param out    已經排列內容
	 * @param target 須要排列的數據集合
	 * @param m      排列元素個數
	 * 
	 * 待解決:1 大數據 溢出 ()  2 使用多線程提速排列過程
	 *    
	 * */
	public static void f(List<String> result, String out, List<String> target, int m) {
			if(m == 0) {
				result.add(out);
				System.out.println(out);
			} else {
				for (int i=0; i<target.size(); i++) {
					List<String> tem = getSubList(target,i);
					f(result, out + target.get(i), tem, m-1);
				}
			}
	}
	/**
	 * 求排除第i個元素的子集
	 * @param target
	 * @param i
	 * @return
	 */
	private static List<String> getSubList(List<String> target, int i) {
		List<String> temp = new ArrayList<String>();
		temp.addAll(target);
		temp.remove(i);
		return temp;
	}

調用:

public static void main(String[] args) {
		List<String> list = new ArrayList<String>();
		
		String[] arr = "1 2 3 4 5 6 7 8 9 0 A B C D E F G".split(" ");
	
		Collections.addAll(list, arr);
		
		List<String> result = new ArrayList<String>();
		
		int len = arr.length;
		int m = 17;
		long timer = System.currentTimeMillis();
		f(result, "", list, m);
		timer = System.currentTimeMillis() - timer;
		System.out.println("A("+m+","+len+") size="+result.size()+" timer="+timer);
		
	}