Answers to Sample Prelim 3 Questions

1.

static int[] rightShift ( int[] a )

{

int n = a.length;

int[] b = new int[ n ];

for( int i = 0; i < n; i++ )

b[ i ] = a[ ( n - 1 + i )%n ];

return b;

}

2.

static int[] delete( int[] a, int x )

{

int numOfXs = 0;

for( int i = 0; i < a.length; i++) if ( a[ i ] == x ) numOfXs++;

int[] b = new int[ a.length - numOfXs ];

for( int i = 0, j = 0; i < a.length; i++ )

if ( a[ i ] != x )

b[ j++ ] = a[ i ];

return b;

}

3.

static boolean isPalindrome( char[] array )

{

int i, n = array.length;

for( i = 0; i < n/2 && ( array[ i ] == array[ n - 1 - i ] ); i++ );

return i == n/2;

}

4.

static int[][] copy( int[][] matrix )

{

int n = matrix.length;

int[][] copy = new int[ n ][ ];

for( int i = 0; i < n; i++ )

{

copy[ i ] = new int[ matrix[ i ].length ];

for( int j = 0; j < matrix[ i ].length; j++ )

copy[ i ][ j ] = matrix[ i ][ j ];

}

return copy;

}

5.

static int[][] rightShift( int[][] matrix )

{

int n = matrix.length;

int[][] ans = new int[ n ][ matrix[ 0 ].length ];

for( int i = 0; i < n; i++ )

for( int j = 0; j < matrix[ i ].length; j++ )

ans[ i ][ j ] = matrix[ ( n - 1 + i )%n ][ j ];

return ans;

}

6.

static double avg( int[][] matrix )

{

int sum = 0, numOfElements = 0;

for( int i = 0; i < matrix.length; i++ )

for( int j = 0; j < matrix[ i ].length; j++ )

{

sum+=matrix[ i ][ j ];

numOfElements++;

}

return ( (double) sum ) / numOfElements;

}

Note: the last solution does not properly handle the case of no input ( a

matrix of zero size )