m n 全排列

n个字符中长度为m的全排列

public class MNPerm {
	public static void main(String[] args) {

		int[] a = { 1, 2, 3 ,4};
		int m=2;
		System.out.println(perm(a, 0,m));
	}

	public static int perm(int[] a, int begin,int m) {
		if (begin == m) {
			for (int i = 0; i < m; i++) {
				System.out.print(a[i] + " ");
			}
			System.out.println();
			return 1;
		}

		int count = 0;
		for (int i = begin; i < a.length; i++) {
			swap(a, begin, i);
			count += perm(a, begin + 1,m);
			swap(a, begin, i);
		}
		return count;
	}

	public static void swap(int[] a, int begin, int end) {
		int temp = a[begin];
		a[begin] = a[end];
		a[end] = temp;
	}
}