"To be Continued" Java Blue Bridge Cup--algorithm training (1) Recursive framework for typical problems

Preparatory exercises (i)

The question of the full arrangement of letters:

1  PackagePackage1;2 3 //to arrange letters in full order4 ImportJava.util.*;5 6  Public classA1 {7 8     StaticList F (String s) {9List LST =NewVector ();Ten  One         //Export A         if(s.length () = = 1) { - Lst.add (s); -             returnlst; the         } -  -         //The following is the similarity of recursion -         /*vectors are very similar to ArrayList, but vectors are synchronous. */ +          for(inti = 0; I < s.length (); i++) { -             Charx =S.charat (i); +             /*the CharAt () method is used to return the character at the specified index. The index range is from 0 to length ()-1. */ A             //start recursion (from the removed I position element recursion) atList t = f (s.substring (0, I) + s.substring (i + 1)); -  -             /* - * str=str.substring (int beginindex), intercept str from the initial letter length of Beginindex string, the remaining string is assigned to STR; -              *  - * str=str.substring (int beginindex,int in * endIndex); intercepts the string from Beginindex to the end of EndIndex in STR and assigns it to STR; -              */ to              for(intk = 0; K < T.size (); k++) { +Lst.add ("" + x +T.get (k)); -             } the         } *         returnlst; $ Panax Notoginseng     } -  the      Public Static voidMain (string[] args) { +List lst = f ("ABC");//Pass in a string and put the elements all in the list A          for(inti = 0; I < lst.size (); i++) { the System.out.println (Lst.get (i)); +         } -     } $}

Method two: (array)

1  PackagePackage1;2 3 //to arrange letters in full order4 //method Two: Array5 ImportJava.util.*;6 7  Public classA1 {8     //AA: Pending Data9     //K: Consider the current position (array subscript)Ten     Static voidFChar[] AA,intk) { One          A         //Export -         if(k==aa.length-1) { - System.out.println (string.valueof (AA)); the             //The AA of the array type is cast to a string type and output -             return;//K reaches the line, cannot continue recursion, program returns -         } -          +          -         //Recursive similarity +         //Start with the number of K, and then switch to the last number in the array (K starts with the first number) A          for(inti=k;i<aa.length;i++) {//I=k, that is, do not miss the situation of non-exchange at{Chart=aa[k];aa[k]=aa[i];aa[i]=t;}//Temptation -f (aa,k+1);//call k+1; let the latter element -{Chart=aa[k];aa[k]=aa[i];aa[i]=t;}//backtrack, swap back. -             //to be tempted, to backtrack immediately after recursion. -         } -     } in  -      to      +      -      Public Static voidMain (string[] args) { theF ("ABC". ToCharArray (), 0);//K starting with the No. 0 one *         /*ToCharArray (): Converts a string into a character array, allowing for individual manipulation of each character*/ $         }Panax Notoginseng      -}

Topic One:

There are n ants on a slender straight pole 100 centimeters long. They have their heads on the left, some facing to the right.
Each ant can only climb along the pole, at a speed of 1 centimeters per second.
When two ants meet, they will turn around at the same time and crawl in the opposite direction.

Of these ants, 1 ants have a cold. And when they meet with other ants, they will infect the ant with the cold.
Please calculate how many ants have a cold when all the ants are climbing away from the pole.

"Data Format"
The first line enters an integer n (1 < n < 50), which represents the total number of ants.
The next line is n a space-separated integer XI ( -100 < Xi <), the absolute value of Xi, indicating the distance the ant leaves the left end of the pole. A positive value indicates a head to the right, a negative value indicates a head to the left, no 0 values appear in the data, and no two ants occupy the same position. Among them, the first data represents the ants catching a cold.

Requires an output of 1 integers, indicating the number of last cold ants.

For example, enter:
3
5-2 8
The program should output:
1

Again, for example, enter:
5
-10 8-20 12 25
The program should output:
3

Topic (ii)

Xiao Ming likes to build a number of bricks recently. A total of 10 blocks, each building has a number, 0~9.

Rules for building blocks:
Each block is placed on top of the other two blocks, and must be smaller than the number of two blocks below.
At the end of the 4-storey pyramid, all the bricks must be used.

Here are the two qualifying methods:

0
1 2
3 4 5
6 7 8 9

0
3 1
7 5 2
9 8 6 4

Would you please calculate how many of these methods are there?

Topic (iii)

Planet X is sending a 5-man observer mission to the W-Star.
which
A country can send up to 4 people.
A maximum of 2 people can be dispatched in country B.
C countries can send up to 2 people.
D countries can send up to 1 people.
A maximum of 1 people can be sent to the E country.
A maximum of 3 people can be dispatched in F countries.
So how many different combinations of the country will eventually be sent to the W-Star's Observer mission?

Title (iv)

A string of known different letters, to make its full arrangement

Topic (v)

There are repeated letters to remove all combinations of M

For example: "AAABBCCCCCCDD" to take all combinations of 3 letters

Title (vi)

A a 2 2 3 3 4 4, altogether 4 pairs of poker. Please line them up.
Requirements: Two A in the middle there are 1 cards, two 2 has 2 cards, two 3 have 3 cards, two 4 with 4 cards.

Please fill in all the required permutations, the smallest dictionary order.
For example: 22aa3344 is smaller than the a2a23344 dictionary sequence. They are not, of course, the answer to the request.

"To be Continued" Java Blue Bridge Cup--algorithm training (1) Recursive framework for typical problems