fig10_46.java

Data StructuresAnd Algorithm Analysis In Java Source Code

    public class Fig10_46
    {
/* START: Fig10_46.txt */
        public static final long INFINITY = Long.MAX_VALUE;

        /**
         * Compute optimal ordering of matrix multiplication.
         * c contains the number of columns for each of the n matrices.
         * c[ 0 ] is the number of rows in matrix 1.
         * The minimum number of multiplications is left in m[ 1 ][ n ].
         * Actual ordering is computed via another procedure using lastChange.
         * m and lastChange are indexed starting at 1, instead of 0.
         * Note: Entries below main diagonals of m and lastChange
         * are meaningless and uninitialized.
         */
        public static void optMatrix( int [ ] c,
                       long [ ][ ] m, int [ ][ ] lastChange ) 
        {
            int n = c.length - 1;

            for( int left = 1; left <= n; left++ )
                m[ left ][ left ] = 0;
            for( int k = 1; k < n; k++ )   // k is right - left
                for( int left = 1; left <= n - k; left++ )
                {
                    // For each position
                    int right = left + k;
                    m[ left ][ right ] = INFINITY;
                    for( int i = left; i < right; i++ )
                    {
                        long thisCost = m[ left ][  i ] + m[ i + 1 ][ right ]
                             + c[ left - 1 ] * c[ i ] * c[ right ];
                        if( thisCost < m[ left ][ right ] )  // Update min
                        {
                            m[ left ][ right ] = thisCost;
                            lastChange[ left ][ right ] = i;
                        }
                    }
                }
        }
/* END */

        public static void main( String [ ] args )
        {
            int [ ] c = { 50, 10, 40, 30, 5 };
            long [ ][ ] m = new long [ 5 ][ 5 ];
            int lastChange[ ][ ] = new int [ 5 ][ 5 ];

            optMatrix( c, m, lastChange );
            for( int i = 1; i <= 4; i++ )
            {
                for( int j = 1; j <= 4; j++ )
                    System.out.print( m[ i ][ j ] + "    " );
                System.out.println( );
            }
            for( int i = 1; i <= 4; i++ )
            {
                for( int j = 1; j <= 4; j++ )
                    System.out.print( lastChange[ i ][ j ] + "    " );
                System.out.println( );
            }
        }
    }