My Java development and learning journey ------ & gt; use a recursive loop algorithm to list all the data counts in the array, ------ Recursion

My Java development and learning journey ------> use a recursive loop algorithm to list all the data counts in the array ------ Recursion

The interview questions are as follows: list all the combinations of numbers in an array, for example, columns 1 and 2 are 1, 2, 12, and 21.

(The interview questions are from the Java programmer interview book.)

The Code is as follows:

Import java. util. arrays; import java. util. using list; import java. util. list;/*** List all the array sets in an array, for example, columns 1 and 2 are 1, 2, 12, 21 */public class ListAll {public static void main (String [] args) {String [] array = new String [] {"1", "2 ", "3"}; listAll (Arrays. asList (array ),"");} /*** use Recursive Method * @ param candidate the List set recursively traversed * @ param prefix the prefix printed */public static void listAll (List <String> candidate, String prefix) {System. out. println (prefix); for (int I = 0; I <candidate. size (); I ++) {List temp = new sort List (candidate); // converts it to the sort List for ease of inserting and moving listAll (temp, prefix + temp. remove (I ));}}}

Output result:

112123131322212132323133131232321

For ease of understanding, add System. out. println ("candidate is:" + candidate) in the loop );

Public static void listAll (List <String> candidate, String prefix) {System. out. println (prefix); for (int I = 0; I <candidate. size (); I ++) {System. out. println ("candidate is:" + candidate); // This line of code is easy to understand recursive List temp = new sort List (candidate); // converts it to the sort List for ease of inserting and moving listAll (temp, prefix + temp. remove (I ));}}

The output result is as follows:

candidate is: [1, 2, 3]1candidate is: [2, 3]12candidate is: [3]123candidate is: [2, 3]13candidate is: [2]132candidate is: [1, 2, 3]2candidate is: [1, 3]21candidate is: [3]213candidate is: [1, 3]23candidate is: [1]231candidate is: [1, 2, 3]3candidate is: [1, 2]31candidate is: [2]312candidate is: [1, 2]32candidate is: [1]321

The algorithm actually has a few numbers and is divided into several groups. For example, if [1, 2, 3], the first layer of recursion is 1-[2, 3], 2-[1, 3], 3-[1, 2]. Next, let's pass in the list and continue recursion. Taking 1-[2, 3] as an example: it can be divided into 2-[3], 3-[2], and splice these with the first layer 1 into 12-[3], 13-[2], and then the list continues recursion, so that all the combinations starting with 1 are arranged. The same is true at the beginning of 2 and 3.

If you want to print a combination of all numbers, such as 123,132,213,231,312,321

Change the code of the listAll Method to the following:

Public static void listAll (List <String> candidate, String prefix) {if (candidate. isEmpty () {System. out. println (prefix);} for (int I = 0; I <candidate. size (); I ++) {// System. out. println ("candidate is:" + candidate); // This line of code is easy to understand recursive List temp = new sort List (candidate); // converts it to the sort List for ease of inserting and moving listAll (temp, prefix + temp. remove (I ));}}

The output is as follows:

123132213231312321

After the annotations are removed, the output is as follows:

candidate is: [1, 2, 3]candidate is: [2, 3]candidate is: [3]123candidate is: [2, 3]candidate is: [2]132candidate is: [1, 2, 3]candidate is: [1, 3]candidate is: [3]213candidate is: [1, 3]candidate is: [1]231candidate is: [1, 2, 3]candidate is: [1, 2]candidate is: [2]312candidate is: [1, 2]candidate is: [1]321

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Author: Ouyang Peng: Welcome to repost. sharing with others is the source of progress!

Reprinted Please retain the original address: http://blog.csdn.net/ouyang_peng

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