[英]Permutation of a Integer in descending order
I am trying to return the permutations of an integer in descending order.我正在尝试按降序返回 integer 的排列。 Currently I have code which returns all the permutations of a number however, it is not in descending order.目前我有返回一个数字的所有排列的代码,但是它不是按降序排列的。 I am unsure to whether I should use an array instead and it may be easier.我不确定是否应该使用数组,它可能更容易。 My current code is:我目前的代码是:
// Function to print all the permutations of str
static void printPermutn(String str, String ans)
{
// If string is empty
if (str.length() == 0) {
System.out.print(ans + " ");
return;
}
for (int i = 0; i < str.length(); i++) {
// 1st character of str
char ch = str.charAt(i);
// Rest of the string after excluding
// the 1st character
String ros = str.substring(0, i) +
str.substring(i + 1);
// Recurvise call
printPermutn(ros, ans + ch);
}
}
You can use global List<String> permutations
then put all values into this collection您可以使用全局List<String> permutations
,然后将所有值放入此集合
Finally, you can sort it in a descending order using最后,您可以使用降序对其进行排序Collections.sort(permutations, Collections.reverseOrder());
private static List<String> permutations;
public static void main(String[] args) {
permutations = new ArrayList<>();
printPermutn("123", "");
System.out.println();
System.out.println("permutations BEFORE sorting");
System.out.println(permutations);
// sort
Collections.sort(permutations, Collections.reverseOrder());
System.out.println("permutations AFTER sorting");
System.out.println(permutations);
}
// Function to print all the permutations of str
static void printPermutn(String str, String ans) {
// If string is empty
if (str.length() == 0) {
System.out.print(ans + " ");
permutations.add(ans);
return;
}
for (int i = 0; i < str.length(); i++) {
// 1st character of str
char ch = str.charAt(i);
// Rest of the string after excluding
// the 1st character
String ros = str.substring(0, i) + str.substring(i + 1);
// Recurvise call
printPermutn(ros, ans + ch);
}
}
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