# ArrayList 1 Excercises

BlueJ users. Read this about how to use ArrayLists as parameters. Or consider using Eclipse if this is too much of a hassle.

ArrayList<Integer> factors(int num)

Description: This method returns an ArrayList populated with the factors of num

 Method Call return value/output factors(5) {1,5} factors(10) {1,2,5,10}

int sum(ArrayList<Integer> nums)

Description: This method returns the sum of all elements in the list

 Method Call return value/output sum({1,5}) 6 sum( { 3,4, 2 }  ) 9

void printReverse(ArrayList<String> strs)

Description: This method prints all elements in reverse order

 Method Call return value/output printReverse({“a”,”b”}) “b” “a” printReverse( “xu”, “t”) “t” “xu”

double mean(ArrayList<Integer> nums)

Description: This method returns the arithmetic mean of all elements in the list

 Method Call return value/output mean({1,5}) 3 mean( {3,4, 2 } ) 4.5

void printEvens(ArrayList<Integer> nums)

Description: This method prints out all even numbers

 Method Call return value/output printEvens({1,5 , 6}) 6 printEvens( {3,4, 2 }  ) 4 , 2

ArrayList<Double> everyOtherPi(ArrayList<Double> nums )

Description: This method returns a version of the input ArrayList with every other value changed to Math.PI

Do NOT make a new ArrayList in this method

 Method Call return value/output everyOtherPi ( {1,8,5,0, 7} ) {1, 3.1415 , 5 , 3.1415 , 7 , 3.1415 } everyOtherPi({0,4,3,5} ) {0, 3.1415 ,  3 , 3.1415 }

boolean isIdentical(ArrayList<String> strs1 , ArrayList<String> strs2)

Description: This method returns true if each element in the two ArrayLists is the same

 Method Call return value/output isIdentical({“ab”, “a”} , { “x”, “a”} ) false isIdentical({“ab”, “a”} , { “ab”, “a”} ) true isIdentical({ “xy”} , { “XY”} ) false

int largest(ArrayList<Integer> nums)

Description: This method returns the largest element in nums

 Method Call return value/output largest({1,5 , 6}) 6 largest ({3,4, 2 }  ) 4

ArrayList<Integer>removeVal(ArrayList<Integer> nums, int val)

Description:This method returns an ArrayList with all instances of val removed

Do NOT make a new ArrayList in this method

 Method Call return value/output removeVal({1,5 , 6}, 5 ) {1, 6 } removeVal  ( {3,3,3,4, 2} , 3 ) {4,2}

TO do :

PrimesFactory

# Matrix Class

Create a class Matrix

int[][] add (int[][] matr1, int[][] matr2)

Description: This method returns the sum of matr1 and matr2

int[][] multiply(int[][] matr1, int[][] matr2)

Description: This method returns the product of matr1 and matr2

# 2 D Arrays in Java Assignments

Add the following Methods to a class called ArrayFun2D

public void print(int[][] arr)

Description: This method prints each element in the array. This will be a useful method when you are debugging your code and want to test it out to see if it works.

 Method Call return value print({{1,2} , {3,4}, { 5, 6 } } ) 1   2 3  4 5   6

public int sum(int[][] arr)

Description: This method returns the sum of all elements in the array

 Method Call return value sum({{1,2} , {3,4}, { 5, 6 } } ) 21 ( ie 1+2+3+4+5+6)

public String concat(String[][] strs)

Description: This method returns the concatenation of all the elements in the Array

 Method Call return value concat({{“a”,”xc” }, {“t”, “zoo”}, { “jjkj” } } ) “axctzzoojjkj”

public double mean( int[][] arr)

Description: This method returns the arithmetic mean of the array. Make sure you double check that you are correctly returning results that include decimal values .

 Method Call return value mean({{2,8} , {4 , 7} } ) 5.25 ie (2+8+4+7)/4

public void printRow(int[][] arr, int row)

Description: This method prints all elements in `row``. ``This can be (and should be) done with a single loop.`

 Method Call return value printRow({{1,2} , {3,4}, { 5, 6 } } , 1 ) 3, 4 printRow( { 5 , 6} , {7, 12, 13 , 5 }, { 5, 6 ,0} } , 2 ) 5 , 6, 0

public void printCol(int[][] arr, int col)

Description: This method prints all elements in `col`

 Method Call return value printCol({{1,2} , {3, 4}, { 5, 6 } } , 1 ) 2 4 6 printCol( { 5 , 6} , {7, 12, 13 , 5 }, { 12, 6 ,0} } , 0 ) 5 7 12 printCol(    {12, 13 , 5 }, { 6, 2, 13 ,11}  , {1,2 } } , 2 ) 5 13

public int maxVal_inRow(int[][] arr, int row)

Description: This method returns the value of the largest number in the given row

 Method Call return value maxVal_inRow({{1,2} , {3,4}, { 5, 6 } } , 1 ) 4 maxVal_inRow ({   { 5 , 6} , {7, 12, 13 , 5 }, { 5, 6 ,0} } , 2 ) 6

public int maxVal_inCol(int[][] arr, int col)

Description: This method returns the value of the largest number in the given col

 Method Call return value maxVal_inCol({{1,2} , {3,4}, { 5, 6 } } , 0 ) 5 maxVal_inCol({{1,-2} , {3,-4}, { 5, -5 } } , 1 ) -2

public int[][] changeValues(int[][] table, int val)

Description:This method returns the array with all elements set to`val`

changeValues(table, 5)

Original Array

 1 2 3 4 5 6
Returned Array

 5 5 5 5 5 5

public void print_colMajor(int[][] arr)

Description: This method prints each element in the array – using column major order

 Method Call return value print({{1,2} , {3,4}, { 5, 6 } } ) 1   3   5 2  4    6

public int[][] removeVals(int[][] table, int val)

Description: This method returns a version of the 2-d array where val has been removed from all elements

removeValues(table, 5)

Original Array

 {1 , 5} {3, 4} {5, 6}
Returned Array

 {1} {3, 4} {6}

int[] twoD_to1D(int[][] arr)

Description: This method takes an input array that is in 2 dimensions  and  creates a 1 d array . Assume that the array is rectangular (not jagged).

 Method Call return value twoD_to1D ( {{1,2} , {3,4}, { 5, 6 } } ) { 1 , 2 ,  3 ,  4 , 5 ,  6 }

## Matrices

int[][] add (int[][] matr1, int[][] matr2)

Description: This method returns the sum of matr1 and matr2

** int[][] multiply(int[][] matr1, int[][] matr2)

Description: This method returns the product of matr1 and matr2

how to multiply matrices

**public int[][] invertValues(int[][] matr)

Description: This method returns the paramater with its values ‘inverted’

Original Array

 1 2 3 4 5 6
Returned Array

 6 5 4 3 2 1

# Two Dimensional Arrays in Java

2-D array Demo Code

2 D Array Assignments

# Array 3 [ v1]

Warming up

public void  printFactors( int n )

Description: This method prints all factors of n

 Method Call return value/output printFactors( 5) 1 5 printFactors( 6) 1 2 3 6 printFactors( 9 ) 1 3 9 printFactors( 15) 1 3 5 15

public int[] getFactors( int n )

Description: This method returns an array populated with the factors on n

 Method Call return value/output getFactors( 5) {1,5} getFactors( 6) {1,2,3,6} getFactors( 9 ) {1,3, 9} getFactors( 15) {1,3,5}

public int[]  removeZeros(int [] nums)

Description: This method returns a version of the input –with all occurrences of 0 , zero, removed

 Method Call return value/output noZeros(  { 3 , 4, 0, 1} ) { 3, 4, 1} noZeros(  { 0, 5 , 0, 0, 9, 0, 1 , 11} ) { 5,9,1,11}

** public int[]  doubleUp( int  [] nums, int val)

Description: This method retuns a version of the input –with all occurances of val  duplicated.

 Method Call return value/output doubleUp(  { 3 , 4, 0, 1}  , 4  ) { 3, 4 , 4, 0, 1} doubleUp(  { 1, 3 , 1, 5 , 3, 3} ,  3 ) {1 , 3, 3  , 1, 5 , 3, 3, 3, 3 }

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