[英]Recursively Print All Subsets Using First 'n' Integers in an Array
Recursively print the possible subsets using the first n integers of an array. 使用数组的前n个整数递归打印可能的子集。 Example: int[] X = [1, 2, 3, 4] and if n = 3, print [3, 2, 23, 1, 13, 12, 123]
示例:int [] X = [1,2,3,4],如果n = 3,则打印[3,2,23,1,13,12,123]
I've sat here for hours, I've tried blindly and am now turning to you guys for some help! 我已经在这里坐了几个小时,我已经盲目尝试,现在正在寻求你们的帮助! Here's what I have so far.
到目前为止,这就是我所拥有的。 Its nowhere near the answer so bear with me.
答案无处可寻,请耐心等待。
static void subsets(int[] A, int n){
subsets("", A, n);
}
private static void subsets(String S, int[] A, int n){
if(n == 0){
System.out.println(S);
} else {
for (int i = n-1; i >= 0; i--) {
subsets(A[n-i-1]+S, A, n-i);
}
}
}
There are many ways to solve this subsets problem, but I particularly like the one below. 有很多方法可以解决此子集问题,但我特别喜欢以下一种方法。
It relies on the fact that, when you count from 1 to N in binary (N being a power of 2) in binary, the bits get through all the possible unique combinations. 它依赖于以下事实:当您以二进制数从1到N计数(N是2的幂)时,这些位会经过所有可能的唯一组合。 So, if you "attach" each bit to a particular value in your array, you get every possible combinations of your values.
因此,如果将每个位“附加”到数组中的特定值,则将获得值的所有可能组合。
In your example, you take N = 3 values in your array. 在您的示例中,您在数组中取N = 3个值。 With N bits, you can get
2^3
(or 1<<3
) = 8 different values. 使用N位,您可以获得
2^3
(或1<<3
)= 8个不同的值。 So let's count from 0 to 7 in binary, and watch the bits that get on or off at each step : 因此,让我们以二进制数从0到7进行计数,并观察每个步骤中打开或关闭的位:
And there you are : you found all possible subsets among your N elements. 在那里,您发现了N个元素中的所有可能子集。
Here is the code : 这是代码:
int[] nums = new int[]{1, 2, 3, 4};
int n = 3;
int maxValueOnNBits = 1 << n;
for (int i = 1; i <= maxValueOnNBits; i++) {
for (int bit = 0; bit < n; bit++) {
int mask = 1 << bit;
if ((i & mask) == mask) System.out.print(nums[bit]);
}
System.out.println();
}
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