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import Color from '../../utils/Color';
import HashStructure from './HashStructure';
/**
* @param array
* @returns {number}
*/
function getFillFactor(array) {
return array.filter((e) => e.occupied).length / array.length;
}
/**
* One Row of the hash table. Holds exactly 1 value.
* @constructor
*/
function Row() {
/**
* The value currently stored in the Row.
* @type {undefined}
*/
this.value = undefined;
/**
* Indicator if there is currently a value stored in this row or not.
* @type {boolean}
*/
this.occupied = false;
/**
* Indicator if there has been a value that is now removed, to
* continue later searches past an empty row.
* @type {boolean}
*/
this.extraCheck = false;
}
/**
* LinearProbing is a hash collision resolution strategy where the first free position after the
* determined position is used to insert the element.
*
* This implementation features lazy deletion, where after the removal of a key the hash table is
* not reorganized, but instead a flag is set that at the position there was a deleted value and
* later searches should continue past this empty slot.
* Extending the table then reorganizes the values to get rid of all deleted values that still
* occupy space in the hash table.
*/
export default class LinearProbing extends HashStructure {
/**
* At what fill factor should the hash table be extended to accommodate more values?
* @type {number}
*/
static MAX_FILL_FACTOR = 0.7;
/**
* By how much should an existing hash table be extended if the max fill factor is reached?
* @type {number}
*/
static EXTEND_FACTOR = 1.3;
/**
* An array of row objects representing the current state of the hash table.
* @type {Row[]}
*/
rows = [];
/**
* The current fill factor of the hash table.
* @type {number}
*/
fillFactor = 0;
/**
* A dynamic hash table extends itself automatically if the specified fill factor is reached.
* Use init(size, false) to disable and thus provoke more hash collisions.
* @type {boolean}
*/
dynamic = true;
/**
* Initialize the hash table.
* @param {number} size
* @param {boolean} dynamic
*/
init(size = 9, dynamic = false) {
const steps = [];
// initialize all rows with a new Row-Object
this.rows = [];
for (let i = 0; i < size; i += 1) {
this.rows.push(new Row());
}
this.fillFactor = 0;
this.dynamic = dynamic;
steps.push({
do: [{
action: Action.CREATE_LINEAR_LIST,
size,
}],
undo: [{
action: Action.DELETE_LINEAR_LIST,
}],
});
steps.push({
do: [{
action: Action.SET_HASH_CALCULATION,
text: 'Address = value % length = ?',
}],
undo: [{
action: Action.SET_HASH_CALCULATION,
text: 'Address = value % length = ?',
}],
});
steps.push({
do: [{
action: Action.SET_FILL_FACTOR,
value: 0,
}],
undo: [{
action: Action.SET_FILL_FACTOR,
value: 'N/A',
}],
});
return steps;
}
/**
* The hash function that is used to determine the position of a given value.
* @param value
* @returns {number}
*/
hash(value) {
return value % this.rows.length;
}
/**
* Extend the hash table to accommodate more values.
*/
extend() {
const steps = [];
const oldValues = this.rows
.filter((e) => e.occupied)
.map((e) => e.value);
const newSize = Math.trunc(this.rows.length * LinearProbing.EXTEND_FACTOR);
steps.push({
do: [{
action: Action.UNSET_EXTRA_CHECK,
index: null,
}],
undo: [{
action: Action.SET_EXTRA_CHECK,
}],
});
steps.push({
do: [{
action: Action.DELETE_LINEAR_LIST,
size: newSize,
}],
undo: [{
action: Action.CREATE_LINEAR_LIST,
size: this.rows.length,
}],
});
steps.push({
do: [{
action: Action.CREATE_LINEAR_LIST,
size: newSize,
}],
undo: [{
action: Action.DELETE_LINEAR_LIST,
size: this.rows.length,
}],
});
steps.push({
do: [{
action: Action.SET_FILL_FACTOR,
value: 0,
}],
undo: [{
action: Action.SET_FILL_FACTOR,
value: this.fillFactor,
}],
});
this.rows = [];
for (let i = 0; i < newSize; i += 1) {
this.rows.push(new Row());
}
this.fillFactor = 0;
oldValues.forEach((oldValue) => {
const insertSteps = this.insert(oldValue);
steps.push(...insertSteps);
});
return steps;
}
/**
* Insert the given value into the hash table.
* @param value
* @return {Object[]}
*/
insert(value) {
const steps = [];
if (this.rows.length === 0) {
// No table created
steps.push({
do: [{
action: Action.NOOP,
text: 'Create a new hash table to insert a value.',
}],
undo: [{
action: Action.NOOP,
text: 'Create a new hash table to insert a value.',
}],
});
return steps;
}
if (this.fillFactor === 1) {
// Table full and static
steps.push({
do: [{
action: Action.NOOP,
text: 'Table is full and static, cannot insert the given value.',
}],
undo: [{
action: Action.NOOP,
text: 'Table is full and static, cannot insert the given value.',
}],
});
return steps;
}
/** @type {number} */
let address = this.hash(value);
steps.push({
do: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = ${value} % ${this.rows.length} = ${address}`,
}],
undo: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = value % ${this.rows.length} = ?`,
}],
});
steps.push({
do: [{
action: Action.SET_POINTER,
index: address,
text: `Set pointer at address ${address}.`,
}],
undo: [{
action: Action.UNSET_POINTER,
index: address,
}],
});
let inserted = false;
while (!inserted) {
if (this.rows[address].occupied) {
// position is occupied.
const undoAction = this.rows[address].extraCheck
? Action.SET_EXTRA_CHECK
: Action.UNSET_EXTRA_CHECK;
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_COLLISION,
text: `Highlight collision at address ${address}.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
steps.push({
do: [{
action: Action.SET_EXTRA_CHECK,
index: address,
}],
undo: [{
action: undoAction,
index: address,
}],
});
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
text: `Unhighlight at address ${address}.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
this.rows[address].extraCheck = true;
// linear probe:
const prevAddress = address; // needed for undo action
address += 1;
if (address === this.rows.length) {
// roll over
address = 0;
}
// We only need to check whether we reached the initial position if the list is full.
// Because we extend at 70% fill rate already, the hash table is never full
// and we won't ever reach the initial position.
steps.push({
do: [{
action: Action.MOVE_POINTER,
index: address,
}],
undo: [{
action: Action.MOVE_POINTER,
index: prevAddress,
}],
});
} else {
// found a position - insert the value.
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_INSERT_SEARCH_COMPLETED,
text: `Found empty position at address ${address}.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
steps.push({
do: [{
action: Action.SET_VALUE,
index: address,
value,
text: `Insert value ${value} at address ${address}.`,
}],
undo: [{
action: Action.SET_VALUE,
index: address,
value: this.rows[address].value,
}],
});
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
text: `Unhighlight inserted element at ${address}.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_INSERT_SEARCH_COMPLETED,
}],
});
this.rows[address].value = value;
this.rows[address].occupied = true;
inserted = true;
steps.push({
do: [{
action: Action.UNSET_POINTER,
index: address,
}],
undo: [{
action: Action.SET_POINTER,
index: address,
}],
});
steps.push({
do: [{
action: Action.SET_FILL_FACTOR,
value: getFillFactor(this.rows),
}],
undo: [{
action: Action.SET_FILL_FACTOR,
value: this.fillFactor,
}],
});
this.fillFactor = getFillFactor(this.rows);
if (this.fillFactor > LinearProbing.MAX_FILL_FACTOR && this.dynamic) {
steps.push({
do: [{
action: Action.NOOP,
text: 'Maximum fill factor reached, need to extend hash table.',
}],
undo: [{
action: Action.NOOP,
text: 'Maximum fill factor reached, need to extend hash table.',
}],
});
const extendSteps = this.extend();
steps.push(...extendSteps);
}
}
}
return steps;
}
/**
* Search for the given value in the hash table.
* @param {number} value
* @return {Object[]}
*/
search(value) {
const steps = [];
if (this.rows.length === 0) {
// no table created
steps.push({
do: [{
action: Action.NOOP,
text: 'Create a new hash table to search for a value.',
}],
undo: [{
action: Action.NOOP,
text: 'Create a new hash table to search for a value.',
}],
});
return steps;
}
const initialAddress = this.hash(value);
let address = initialAddress;
steps.push({
do: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = ${value} % ${this.rows.length} = ${address}`,
}],
undo: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = value % ${this.rows.length} = ?`,
}],
});
steps.push({
do: [{
action: Action.SET_POINTER,
index: address,
text: `Set pointer at address ${address}.`,
}],
undo: [{
action: Action.UNSET_POINTER,
index: address,
}],
});
let found = false;
while (!found) {
if (this.rows[address].occupied && this.rows[address].value === value) {
// found value, done.
found = true;
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_INSERT_SEARCH_COMPLETED,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
break;
}
if (this.rows[address].extraCheck === false) {
// not occupied or wrong value, and no indication to continue search
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_COLLISION,
text: 'No extra check.',
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
text: 'No extra check.',
}],
});
break;
}
// needed for undo action
const prevAddress = address;
address += 1;
if (address === this.rows.length) {
// wrap around
address = 0;
}
if (address === initialAddress) {
// reached beginning, not found
steps.push({
do: [{
action: Action.NOOP,
text: 'Value not found - Searched the entire hash table.',
}],
undo: [{
action: Action.NOOP,
}],
});
break;
}
steps.push({
do: [{
action: Action.MOVE_POINTER,
index: address,
}],
undo: [{
action: Action.MOVE_POINTER,
index: prevAddress,
}],
});
}
steps.push({
do: [{
action: Action.UNSET_POINTER,
index: address,
}],
undo: [{
action: Action.SET_POINTER,
index: address,
}],
});
if (found) {
// found
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
text: `The value ${value} was found in the hash table at address ${address}.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_INSERT_SEARCH_COMPLETED,
text: `The value ${value} was found in the hash table at address ${address}.`,
}],
});
} else {
// not found
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
text: `The value ${value} was not fund in the hash table.`,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_COLLISION,
text: `The value ${value} was not fund in the hash table.`,
}],
});
}
return steps;
}
/**
* Remove the given value from the hash table.
* @param value
* @return {{}[]}
*/
remove(value) {
const steps = [];
if (this.rows.length === 0) {
// no table created
steps.push({
do: [{
action: Action.NOOP,
text: 'Create a new hash table to delete a value.',
}],
undo: [{
action: Action.NOOP,
text: 'Create a new hash table to delete a value.',
}],
});
return steps;
}
const initialAddress = this.hash(value);
let address = initialAddress;
steps.push({
do: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = ${value} % ${this.rows.length} = ${address}`,
}],
undo: [{
action: Action.SET_HASH_CALCULATION,
text: `Address = value % ${this.rows.length} = ?`,
}],
});
steps.push({
do: [{
action: Action.SET_POINTER,
index: address,
text: `Set pointer at address ${address}.`,
}],
undo: [{
action: Action.UNSET_POINTER,
index: address,
}],
});
let found = false;
while (!found) {
if (this.rows[address].occupied && this.rows[address].value === value) {
// found value, remove, done.
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.HASH_INSERT_SEARCH_COMPLETED,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
steps.push({
do: [{
action: Action.SET_VALUE,
index: address,
value: null,
}],
undo: [{
action: Action.SET_VALUE,
index: address,
value,
}],
});
steps.push({
do: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
undo: [{
action: Action.SET_COLOR,
index: address,
color: Color.BASE_COLOR_HASH_TABLE,
}],
});
this.rows[address].value = undefined;
this.rows[address].occupied = false;
this.rows[address].extraCheck = true;
steps.push({
do: [{
action: Action.SET_FILL_FACTOR,
value: getFillFactor(this.rows),
}],
undo: [{
action: Action.SET_FILL_FACTOR,
value: this.fillFactor,
}],
});
this.fillFactor = getFillFactor(this.rows);
found = true;
break;
}
if (this.rows[address].extraCheck === false) {
// not occupied or wrong value, and no indication to continue search
steps.push({
do: [{
action: Action.NOOP,
text: 'No extra check.',
}],
undo: [{
action: Action.NOOP,
text: 'No extra check.',
}],
});
break;
}
const prevAddress = address; // needed for undo action
address += 1;
if (address === this.rows.length) {
// wrap around
address = 0;
}
if (address === initialAddress) {
// reached beginning, not found
steps.push({
do: [{
action: Action.NOOP,
text: 'Searched the entire hash table.',
}],
undo: [{
action: Action.NOOP,
text: 'Searched the entire hash table.',
}],
});
break;
}
steps.push({
do: [{
action: Action.MOVE_POINTER,
index: address,
}],
undo: [{
action: Action.MOVE_POINTER,
index: prevAddress,
}],
});
}
steps.push({
do: [{
action: Action.UNSET_POINTER,
index: address,
}],
undo: [{
action: Action.SET_POINTER,
index: address,
}],
});
if (found) {
// removed
steps.push({
do: [{
action: Action.NOOP,
text: `The value ${value} was found at address ${address} and removed from the hash table.`,
}],
undo: [{
action: Action.NOOP,
text: `The value ${value} was found at address ${address} and removed from the hash table.`,
}],
});
} else {
// not removed
steps.push({
do: [{
action: Action.NOOP,
text: `The value ${value} was not fund in the hash table and therefore not removed.`,
}],
undo: [{
action: Action.NOOP,
text: `The value ${value} was not fund in the hash table and therefore not removed.`,
}],
});
}
return steps;
}
}
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