CS 110 Arrays II Multi dimensional Arrays 1 Organize information in a way that solves more complex problems than can be done with a linear or one dimensional array 2 dimensioanl array matrix o simplest o Table o All elements must be of the same data type o Fixed size Examples o Classroom seating chart 6 desk in a row with 5 rows X X X X X X X X X X X X X X X X X X X X X X X X X X X X X X String desk new String 5 6 o Employee Time time Emp Mon Tues Wed Thurs Fri Sat Sun double timeCard new double 30 7 o Girl Scout Cookie Orders Customer ThinMints DoSiDoes Treffoils int cookieOrders new int customers 3 Reference a element Need both row and column index matrix r c desk 0 5 the student s name in the first row door seat cookieOrder 3 0 the number of ThinMints customer 3 ordered custTotal 0 for int i 0 i 3 i custTotal cookieOrder 3 i Copyright C Tanner 2010 CS 110 Arrays II Multi dimensional Arrays Memory Allocation of 2 dimensional Arrays Initialization when declared o double matrix 3 2 4 2 1 0 5 7 6 1 0 0 Creates 2 3 Processing o Nested loops o For each row For each col Process element r c o 0 0 0 1 0 2 1 0 1 2 etc o Row major order o If we switch the loops then we process in column major order Sum the elements int sumMatrix int matrix int sum 0 for int r 0 r matrix length r 0 for int c 0 c matrix r length c sum matrix r c return sum Determining the length of the matrix o Allows for general purpose algorithms o row arrayName length o col arrayName row length Must do this because each row is an array itself Copyright C Tanner 2010 2 CS 110 Arrays II Multi dimensional Arrays 3 Write a general purpose method to print a 2 dimensional array in table format void printMatrix int matrix for int r 0 r matrix length r for int c 0 c matrix r legnth c 0 System out print matrix r c System out println Arrays with more than 2 dimensions o No limit on the number of dimensions o Consider monthly sales for last 5 years for each salesperson sales person years months Programming Problem Jet Propulsion Laboratory Take matrix representing digitized representation of night sky and locate stars on it Each element of the array represents the amount of light hitting that portion of the image when the picture was taken Intensities range from 0 20 A star is located in i j element area if intense i j sum of surrounding 4 5 6 0 6 x 8 section 0 3 4 0 0 0 6 5 13 6 0 0 0 2 2 6 2 7 3 0 10 0 0 4 15 4 1 6 0 0 7 12 6 9 10 5 0 6 10 6 4 8 Copyright C Tanner 2010 8 3 0 0 4 0 ignoring edges 1 1 13 0 1 1 0 2 1 1 2 CS 110 Arrays II Multi dimensional Arrays 4 Adjacent Elements i 1 j i j 1 i j i 1 j Sample Program Stars java Copyright C Tanner 2010 i j 1
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