Linear Data Structure (JS)

JavaScript syntax

Array

  • Insertion / Deletion / Search – O(n)

  • Get / Set – O(1)

const arr = Array(5).fill(0); //[0,0,0,0,0]
arr.fill(1, 2, 4); // [0,0,1,1,0] fill from 2 to 4(exclude)
let len = arr.length;
arr.reverse(); // [0,1,1,0,0] reverse order
arr.sort(); // [0,0,0,1,1] sort array
arr.splice(1, 0, 3); //[0,3,0,1,1] insert 3 at position 1
arr.splice(2, 1, 2); //[0,3,2,1,1] replace 1 element at position 2
arr.concat([6,6]); //[0,3,2,1,1,6,6] merge two arrays
arr.includes(6); //true
arr.indexOf(5); //-1 not found
arr.join(); //"0,3,2,1,1,6,6", join all elements to a string, default comma
arr.join(''); //"0321166"
arr.lastIndexOf(1); //4, return -1 if not found
arr.slice(2); //[2,1,1,6,6]
arr.slice(2, 4); //[1,6] shallow copy, from 2 to 4(exclude)
arr.toString(); // "1,6"

Stack

Last-In First-Out(LIFO)

  • Push / Pop – O(1)

  • Access / Search – O(n)

const stack = ['k'];
stack.push('a');    //insert to the end ['k','a']
stack.pop();        //remove and return last element ['k']
stack.unshift('b'); //insert to the front ['b','k']
stack.shift();      //remove and return first element ['k']

Queue

First-In First-Out(FIFO)

  • Enqueue: insert to the end – O(1)

  • Dequeue: remove and return front element – O(1)

  • Access / Search – O(n)

const queue = ['k'];
queue.unshift('a');  // ['a','k'] insert to the front
queue.pop();         // ['a'] remove last

Linked List

  • Get / Set – O(n)

  • Insert / Remove – O(1)

  • Singly Linked List: no space overflow(compare to array)

    • element

    • link to the next node

  • Doubly Linked List: has special header and trailer, insert/deletion may be O(1) depends on the location.

    • element

    • link to the previous node

    • link to the next node 

 function ListNode(val) {
     this.val = val;
     this.next = null;
 }

JS Iteration Methods 

const arr = [1,2,3];

/* return a new Array Iterator object contain key/value pairs for each index */
let iter1 = arr.entries().next().value; // Array [0, 1]
/* return a new Array Iterator object contain keys for each index */
let iter2 = arr.keys().next().value; // 0
/* return a new Array Iterator object contain values for each index */
let iter3 = arr.values().next().value; // 1

/* test whether all elements satisfies the condition,always true if [] */
arr.every(val => val > 2); //false
/* return true if at least one elements satisfies the condition, always false if [] */
arr.some(val => val > 2); //true

/* return value of first element satisfies the condition, o.w. return undefined */
arr.find(val => val > 0); // 1
/* return index of first element satisfies the condition, -1 if not found */
arr.findIndex(val => val > 0); // 0

/* execute function for each element, in-place */
arr.forEach(val => val + 2); //[3,4,5]
/* create a new array with result of calling function for each element */
const arr2 = arr.map(val => val * 2); //[6,8,10]
/* return new array with all elements pass the test. */
const fil = arr.filter(val => val > 1); //[2,3]
/* execute a reducer function on each element, single output value */
arr2.reduce((accumulator, cur) => accumulator + cur)); // 24, init val = first element
arr2.reduce((accumulator, cur) => accumulator + cur), 6); // 30, init val = 6

JavaScript Loop

for...in statement

let arr = [3, 5, 7], sum = 0;
// iterates over all enumerable properties of an object
for (let i in arr) {
    sum += arr[i] //i = 0, 1, 2
}

for...of statement

let arr = [3, 5, 7], sum = 0;
// loop iterates over iterable objects
for (let i of arr) { 
    sum += i; //i = 3, 5, 7
}

for statement 

for(let i = 0; i < arr.length; i++) {}

do...while statement

let i = 0;
do {
    i++;
}while(i < 5);

while statement

let x = 0;
while (x < 10) {
    x++;
}

labeled statement 

mark: x += 2; 
break;  //like in switch loop

JavaScript Function

const nums = [3,4,2,1,6];
/* call a function this a given this value and an array argument */
let max = Math.max.apply(null,numbers); //6
/* call a function this a given this value and an argument list */
let min = Math.min.call(null,4,3,2); //2
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