About sparse array

First, why use a sparse array?

For example, this board, if you want to record the position of the black and blue pieces of first think of using a two-dimensional array, we built the two-dimensional array (1 black, 2 blue) and found a lot of empty space wasting a lot of memory space

We can use this time to store a sparse array " valid data "

Second, how to use sparse arrays

A total of three sparse array (fixed column), respectively the row number, column number and value

The first line: the initial array of rows, columns, RMS (meaningful values)

Other lines: Successive recording of rms line number, column number and value

The figure shows that the number of rows of the sparse array RMS (effective value assumed num) num + 1, column number 3

Third, code implementation

Sparse array turn ideas:

Define a good array, and assign
Through the array to get the number of valid num
Defines the sparse array, the number of lines num + 1, the number of columns 3, the first row of the array Assignment
Again initial traverse an array, to obtain a valid value assigned to the sparse array
Definition is complete

Sparse array to a two-dimensional array:

Define a two-dimensional array of rows and columns of the first row is read from the sparse array
Setting cycle, according to a few lines later to restore the sparse array

Code:

  1 int [] [] = array1 new new int [. 11] [. 11 ];
   2 // array assigned a black, blue 2 
  . 3 array1 [1] [2] = 1 ;
   . 4 array1 [2] [. 3 ] = 2 ;
   5 // iterate 
  . 6 for ( int [] Row: array1) {
   . 7      for ( int Item: Row) {
   . 8 of System.out.print (Item + "\ T" );
   . 9      }
  10      the System.out. the println ();
  . 11 }
  12 is int NUM = 0 ;
  13 is // iterate again, to find the actual existence of a few number of 
 14  for ( int I = 0; I <. 11; I ++ ) {
  15      for ( int J = 0; J <. 11; J ++ ) {
  16          IF (array1 [I] [J] = 0! {)
  . 17 NUM ++ ;
  18 is          }
  . 19      }
  20 is }
  21 is System.out.println ( "NUM =" + NUM);
  22 is 
 23 is // begin defining the sparse array 
 24 int [] [] = Sparse_array new new  int [NUM +. 1] [. 3 ];
  25 Sparse_array [0] [0] =. 11 ;
  26 is Sparse_array [0] [. 1] =. 11 ;
  27 Sparse_array [0] [2] =NUM;
  28 
 29 // again traverse the sparse array assignment 
 30 int COUNT = 0 ;
  31 is for ( int I = 0; I <. 11; I ++ ) {
  32      for ( int J = 0; J <. 11; J ++ ) {
  33 is          IF (! array1 [I] [J] = 0 ) {
  34 is COUNT ++ ;
  35 Sparse_array [COUNT] [0] = I;
  36 Sparse_array [COUNT] [. 1] = J;
  37 [Sparse_array [COUNT] [2] = array1 [I ] [J];
  38 is          }
  39      }
  40 }
  41 is
 42 // output sparse array 
 43 System.out.println ( "+++++++++++++++++++++ sparse array +++++++++++++ + " );
  44 is for ( int I = 0; I <Sparse_array.length; I ++ ) {
  45 System.out.printf ("% D \ D% T \ T% D \ T \ n-", Sparse_array [I] [ 0], Sparse_array [I] [. 1], Sparse_array [I] [2 ]);
  46 is }
  47 System.out.println ();
  48 
 49 // sparse array recovery 
 50 int [] [] = array2 new new  int [Sparse_array [0] [0]] [Sparse_array [0] [. 1 ]];
  51 is // sparse array and assign loop 
 52 is for ( int. 1 = I; I <Sparse_array.length; I ++) {
  53 is array2 [Sparse_array [I] [0]] [Sparse_array [I] [. 1]] = Sparse_array [I] [2 ];
  54 is }
  55 
 56 is // displayed recovered array 
 57 System.out.println ( "+ +++++++++++++++++ recovered array +++++++++++++++ " );
  58 for ( int [] Row: array2) {
  59      for ( int Item: Row) {
  60 System.out.printf (Item + "\ T" );
  61 is      }
  62 is      System.out.println ();
  63 is }
  64 
 65

About Assignment understood as a sparse array:

count++;
Sparse_array[count][0]=i;
Sparse_array[count][1]=j;
Sparse_array[count][2]=array1[i][j];

Why count?

We are a progressive assignment cycle, when his party assignment, will become only the column, so the definition of a count locking row

After reading the article is Shangxue Tang teacher after class Hanshun Ping sparse array to write, write down hopes to strengthen at the memory