[洗牌算法] - 从长度为m的int数组中随机取出n个元素，每次取的元素都是之前未取过的

//O(N^2)time
//O(N)space
void test(int n, int m) {
    List<Integer> list = new ArrayList<>();
    for (int i = 1; i <= n; i++) {
        list.add(i);
    }
    for (int i = 0; i < m; i++) {
        int t = (int) (list.size() * Math.random());
        System.out.println(list.remove(t));
    }
}

//O(N)time
//O(N)space
void knuth(int n, int m) {
    int[] arr = new int[n];
    for (int i = 0; i < n; i++) {
        arr[i] = i + 1;
    }
    for (int i = 0; i < m; i++) {
        int index = (int) ((n - i) * Math.random());
        System.out.println(arr[i + index]);
        swap(arr, i, i + index);
    }
}

void swap(int[] arr, int i, int index) {
    if (i == index) return;
    int temp = arr[i];
    arr[i] = arr[index];
    arr[index] = temp;
}