如何获得Java中具有重复项的所有组合(递归)? [英] How I can get all combinations that have duplicates in Java (recursion)?
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问题描述
我需要找到一种从这样的组合中删除重复项的方法:
I need to find a way to remove duplicates from a combination like this:
输入: 3和2,其中3是范围(从1到3),而2是每种组合的长度
Input: 3 and 2, where 3 is the range (from 1 to 3) and 2 is the length of each combination
输出: {1,1} {1,2} {1,3} {2,1} {2,2} {2,3} {3,1} {3,2} {3,3}
预期输出: {1,1} {1,2} {1,3} {2,2} {2 ,3} {3,3}
所以我们从 {1,1}->开始{1,2}-> {1,3}->
,但 {2,1}
是 {1,2}
,所以我们忽略它,依此类推。
So we start with {1, 1} -> {1, 2} -> {1, 3} ->
but {2, 1}
is a duplicate of {1, 2}
so we ignore it and so on.
这是我的代码:
import java.util.Scanner;
public class Main {
private static int[] result;
private static int n;
private static void printArray() {
String str = "( ";
for (int number : result) {
str += number + " ";
}
System.out.print(str + ") ");
}
private static void gen(int index) {
if (index == result.length) {
printArray();
return;
}
for (int i = 1; i <= n; i++) {
result[index] = i;
gen(index + 1);
}
}
public static void main(String[] args) {
Scanner input = new Scanner(System.in);
System.out.print("From 1 to: ");
n = input.nextInt();
System.out.print("Length: ");
int k = input.nextInt();
result = new int[k];
gen(0);
}
}
推荐答案
您可以将上次使用的最大值传递给 gen
:
You can pass the last max value used into gen
:
private static void gen(int index, int minI) {
if (index == result.length) {
printArray();
return;
}
for (int i = minI; i <= n; i++) {
result[index] = i;
gen(index + 1, i);
}
}
并以开头1
: gen(0,1);
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