Turn: Java Recursive algorithm example summary

First, the basic idea of recursive algorithm design is:

For a complex problem, the original problem is decomposed into a number of relatively simple and similar sub-problems, continue until the sub-problem is simple enough to be solved directly, that is, to the recursive exit, so that the original problem has a recursive solution.

In the recursive algorithm, it is necessary to grasp the exit, that is, to do recursive algorithm must have a definite recursive end condition. This is very important. In fact, this export is very well understood, is a condition, when we meet the conditions of the time we will no longer be recursive.

The key thing to catch is:
(1) Recursive export

(2) The ground pushes towards the exit gradually

Second, recursive algorithm example

(1) Factorial:

Requirement: Given a number, calculate its factorial value, for example, the factorial of 5 is 5*4*3*2*1

Realize:

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2. <span style="FONT-SIZE:12PX;" >//using recursion to implement a number's factorial value
4. private static BigDecimal Getnum (BigDecimal innum) {
6. if (Innum.compareto (bigdecimal.one) = = 0) {
8. return innum;
10. }
12. Return innum.multiply (Getnum (Innum.subtract (Bigdecimal.one));
14. }</span>

(2) Fibonacci series: 1,1,2,3,5,8,13 ...

Requirements: Find the value of the specified index position in the series

Realize:

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2. <span style="FONT-SIZE:12PX;" >//using recursion to implement the Fibonacci sequence
4. private static int fab (int index) {
6. if (index = = 1 | | index = = 2) {  
8. return 1;
10. } else {
12. Return Fab (index-1) + fab (index-2);
14. }
16. }</span>

(3) Hanoi

Requirements: Hanoi

Realize:

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2. <span style=>  <span  style= "White-space:pre" >   </span>private static final  string disk_b =  "DiskB";   
4. <span style="White-space:pre"> </span>private static final String   Disk_c = "DISKC";
6. <span style="White-space:pre"> </span>private static final  String disk_a = "Diska";
8. <span style="White-space:pre"> </span>static String from=disk_  A
10. <span style="White-space:pre"> </span> static String to=   Disk_c;
12. <span style="White-space:pre"> </span> static String mid=disk_b;
16. <span style="White-space:pre"> </span> public static void Main (String [] args) {
18. <span style= "White-space:pre" >  </ span>      string  input=joptionpane.showinputdialog ("Please input  the number of the disks you want me move. ");   
20. <span style="White-space:pre"> </span> int num=integer.parseint (  Input);
22. <span style="White-space:pre"> </span> Move (num,from,mid,to);
24. <span style="White-space:pre"> </span>}</span>

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2. <span style="FONT-SIZE:12PX;" >//Using recursion to implement Hanoi
4. private static void move (int num, string from2, String Mid2, String to2) {
6. if (num = = 1) {
8. SYSTEM.OUT.PRINTLN ("Move Disk 1 from" + From2 + "to" + To2);
10. } else {
12. Move (Num-1, From2, To2, MID2);
14. SYSTEM.OUT.PRINTLN ("Move disk" + num + "from" + From2 + "to" + To2);
16. Move (Num-1, Mid2, From2, To2);
18. }
20. }</span>

(4) Permutations and combinations

Requirements: Sorts and outputs all elements of a string entered, for example: The parameter you give is "ABC",

The program will output

Abc
Acb
Bac
Bca
Cab
Cba

Realize:

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2. <span style=><span style=< Span class= "Attribute-value" > "White-space:pre" >     </span>public static void permute (String  STR)  {  
4. <span style="White-space:pre"> </span> char[] strarray =   Str.tochararray ();
6. <span style="White-space:pre"> </span> Permute (strarray, 0,  STRARRAY.LENGTH-1);
8. <span style="White-space:pre"> </span;}</span>

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2. <span style="FONT-SIZE:12PX;" >//Use recursive implementations to sort and output all elements of a string entered
4. public static void Permute (char[] list, int. Low, int.) {
6. int i;
8. if (low= = high) {
10. String cout = "";
12. for (i = 0; I <= high; i++) {
14. cout + = List[i];
16. }
18. System.out.println (cout);
20. } else {
22. for (i = Low , I <= high; i++) {
24. Char temp = List[low];
26. List[low] = List[i];
28. List[i] = temp;
30. Permute (list, low + 1, high);
32. temp = List[low];
34. List[low] = List[i];
36. List[i] = temp;
38. }
40. }
42. }</span>

Summing up the recursive algorithm, this root is the exit, as long as the exit is found, then the algorithm will naturally be the natural.

Reference one: http://blog.csdn.net/lfsf802/article/details/7696405

Reference Two, http://nevergives.blog.sohu.com/95934843.html

Turn: Java Recursive algorithm example summary