text: c = cost when keys [ r ] becomes root of this subtree
code: int c = ( ( r > i ) ? cost [ i ] [ r - 1 ] : 0 ) + ( ( r < j ) ? cost [ r + 1 ] [ j ] : 0 ) + sum ( freq , i , j ) ; if ( c < cost [ i ] [ j ] ) cost [ i ] [ j ] = c ; } } } return cost [ 0 ] [ n - 1 ] ; }