java组合算法

/**
	 * 从n个数字中选择m个数字
	 * 
	 * @param a
	 *            传入的要选择的数字数组
	 * @param m
	 *            要选择的个数
	 * @return
	 * @throws Exception
	 */
	public static List<int[]> combine(int[] a, int m) throws Exception {
		int n = a.length;
		if (m > n) {
			throw new Exception("错误！数组a中只有" + n + "个元素。" + m + "大于" + 2 + "!!!");
		}
		List<int[]> result = new ArrayList<int[]>();
		if(m==n){
			result.add(a);
			return result;
		}
		int[] bs = new int[n];
		for (int i = 0; i < n; i++) {
			bs[i] = 0;
		}
		// 初始化
		for (int i = 0; i < m; i++) {
			bs[i] = 1;
		}
		boolean flag = true;
		boolean tempFlag = false;
		int pos = 0;
		int sum = 0;
		// 首先找到第一个10组合，然后变成01，同时将左边所有的1移动到数组的最左边
		do {
			sum = 0;
			pos = 0;
			tempFlag = true;
			result.add(print(bs, a, m));

			for (int i = 0; i < n - 1; i++) {
				if (bs[i] == 1 && bs[i + 1] == 0) {
					bs[i] = 0;
					bs[i + 1] = 1;
					pos = i;
					break;
				}
			}
			// 将左边的1全部移动到数组的最左边

			for (int i = 0; i < pos; i++) {
				if (bs[i] == 1) {
					sum++;
				}
			}
			for (int i = 0; i < pos; i++) {
				if (i < sum) {
					bs[i] = 1;
				} else {
					bs[i] = 0;
				}
			}

			// 检查是否所有的1都移动到了最右边
			for (int i = n - m; i < n; i++) {
				if (bs[i] == 0) {
					tempFlag = false;
					break;
				}
			}
			if (tempFlag == false) {
				flag = true;
			} else {
				flag = false;
			}

		} while (flag);
		result.add(print(bs, a, m));
		return result;
	}

	private static int[] print(int[] bs, int[] a, int m) {
		int[] result = new int[m];
		int pos = 0;
		for (int i = 0; i < bs.length; i++) {
			if (bs[i] == 1) {
				result[pos] = a[i];
				pos++;
			}
		}
		return result;
	}