Implement a custom SparseMatrix class using a custom CustomHashMap class. A sparse matrix is a type of matrix where most of its elements are zero or have no significant value. Sparse matrices are used in various computational applications to save memory and computational effort, as it is more efficient to store and process only non$-$zero elements. Use the skeleton code below.

class CustomHashMap:

def $\_\_$init$\_\_($self$,$size$=997)$:

$"""$

Initializes the hash table with a given size.

:param size: Size of the hash table.

$"""$

self.size $=$size

self.table $=[$None$]*$size

def hash$($self$,$key$)$:

$"""$

Hashes the key to an index in the table.

:param key: The integer key to hash.

:return: An index in the range of the table size.

$"""$

pass

def set$($self$,$key$,$ value$)$:

$"""$

Sets the value at the hashed index for the given key.

:param key: The integer key.

:param value: The float value to store.

$"""$

pass

def get$($self$,$key$)$:

$"""$

Retrieves the value for the given key.

:param key: The integer key to retrieve the value for.

:return: The float value associated with the key, or None if

not found.

$"""$

pass

def display$($self$)$:

$"""$

Displays the hash table contents.

$"""$

pass

class SparseMatrix:

def $\_\_$init$\_\_($self$,$rows$,$ cols$)$:

$"""$

Initializes a sparse matrix using CustomHashMap.

:param rows: Number of rows in the matrix.

:param cols: Number of columns in the matrix.

$"""$

pass

def $\_$get$\_$key$($self$,$row$,$ col$)$:

$"""$

Generates a unique key for the given row and column.

:param row: Row index.

:param col: Column index.

:return: An integer key.

$"""$

pass

def set$($self$,$row$,$ col, value$)$:

$"""$

Sets a value in the sparse matrix.

:param row: Row index.

:param col: Column index.

:param value: Float value to set.

$"""$

pass

def get$($self$,$row$,$ col$)$:

$"""$

Gets a value from the sparse matrix.

:param row: Row index.

:param col: Column index.

:return: Float value at the given position, or None if not

set.

$"""$

pass

def to$\_$dense$($self$)$:

$"""$

Converts the sparse matrix to a dense $2$D list

representation.

:return: $2$D list representing the matrix.

$"""$

pass

def $\_\_$add$\_\_($self$,$other$)$:

$"""$

Adds two sparse matrices of the same dimensions.

:param other: SparseMatrix to add.

:return: A new SparseMatrix representing the sum.

$"""$

pass

def $\_\_$sub$\_\_($self$,$other$)$:

$"""$

Subtracts another sparse matrix from this one.

:param other: SparseMatrix to subtract.

:return: A new SparseMatrix representing the difference.

$"""$

pass

def display$($self$)$:

$"""$

$"""$

Displays the sparse matrix in a readable format.

pass