Hi in my first nodejs interview interviewer ask me to remove all duplicate elements from an unsorted array without using any inbuilt function using java script in minimum TC and without using any other array.

This is my efforts.

 var input = [1, 2, 3, 3, 4, 5,2, 6,3,6,1];
var current = input[0];
var found = false;
function removeDuplicate() {
    for (var i = 0; i < input.length; i++) {
        if (current == input[i]) {
            //found = false;
        } else if (current != input[i]) {
            console.log(" " + current);
            current = input[i];
            found = false;
        }
    }
    console.log(" " + current);

}
removeDuplicate();

Hi in my first nodejs interview interviewer ask me to remove all duplicate elements from an unsorted array without using any inbuilt function using java script in minimum TC and without using any other array.

This is my efforts.

 var input = [1, 2, 3, 3, 4, 5,2, 6,3,6,1];
var current = input[0];
var found = false;
function removeDuplicate() {
    for (var i = 0; i < input.length; i++) {
        if (current == input[i]) {
            //found = false;
        } else if (current != input[i]) {
            console.log(" " + current);
            current = input[i];
            found = false;
        }
    }
    console.log(" " + current);

}
removeDuplicate();

• javascript
• node.js

• Is this a question? if so, what's the question? – StudioTime Commented Jul 19, 2017 at 9:00
• Can't be done. You have to use splice, slice or something similar to modify the array in place, and you have to use indexOf, lastIndexOf or includes to check for dupes, and thet are all native inbuilt array methods. – adeneo Commented Jul 19, 2017 at 9:01
• 1 @adeneo dont you think that splice, slice or whatever have been made using pure javascript? So i m pretty sure it can be done without using it – kikiwie Commented Jul 19, 2017 at 9:05
• No, those methods are written in C++ or whatever the engine is written in. Not all built-ins can be replicated in JS, escpecially when you can't use other built in methods to do so. – adeneo Commented Jul 19, 2017 at 9:32

5 Answers 5

I don't really understand precisely what inbuild functions are or to what extent is a function inbuilt, so I'm assuming I'm not allowed to use indexOf, hasOwnProperty, Array.prototype.push, ...

const input = [1, 2, 3, 3, 4, 5,2, 6,3,6,1];

function removeDuplicate(arr) {
    const result = [];
    let idx = 0;
    const tmp = {};

    for (let i = 0; i < arr.length; i++) {
        if (!tmp[arr[i]]) {
            tmp[arr[i]] = 1;
            result[idx] = arr[i];
            idx++;
        } 
    }
    return result;
}

console.log(removeDuplicate(input));

If you want to remove the elements in place, then the best I can do is save the elements in place, and give the length of the eventual array. But in JavaScript, it's actually valid since arrays in JavaScript are just objects that are enumberable with an extra property length.

const input1 = [1, 2, 3, 3, 4, 5,2, 6,3,6,1];
const input2 = [1, 2, 3, 3, 4, 5,2, 6,3,6,7];

function removeDuplicate(arr) {
    let length = 0;
    const tmp = {};

    for (let i = 0; i < arr.length; i++) {
        if (!tmp[arr[i]]) {
            tmp[arr[i]] = 1;
            arr[length] = arr[i];
            length++;
        }
    }
    
    // the last element is not a duplicate
    if (!tmp[arr[arr.length-1]]) {
        length--;
    }
    arr.length = length;
    return arr;
}

console.log(removeDuplicate(input1));
console.log(removeDuplicate(input2));

One line of vanilla JavaScript with no loops

Since this seems like a homework then at least make some effort to make the solution interesting.

This is my first solution but it uses a built-in .filter() method:

const removeDuplicate = (c=>a=>a.filter(e=>!(c[e]||(c[e]=1)&&0)))({});

Here is another solution without using built-ins:

const f = (c=>(h,...r)=>h?(c[h]|=0)||c[h]++?f(...r):[h,...f(...r)]:[])({});
const removeDuplicate = a => f(...a);

Here you go. One line of vanilla JavaScript plus a convenience wrapper- the second line is so you can use:

console.log(removeDuplicate(input));
// or with literals:
console.log(removeDuplicate([1, 2, 3, 3, 4, 5, 2, 6, 3, 6, 1]));

but if you're fine with this:

console.log(f(...input));
// or with literals:
console.log(f(1, 2, 3, 3, 4, 5, 2, 6, 3, 6, 1));

then you can remove the second line (and of course rename f to something better).

var arr=[
{id: 1, "name": "kumar"}, 
{id: 1, "name": "kumar"}, 
{id: 2, "name": "kumar1"}, 
{id: 2, "name": "kumar1"}, 
{id: 3, "name": "kumar2"}
];
var res=[];
var count={};
arr.forEach((el,ind)=>{
   count[el.id]=(count[el.id] || 0)+1;
   if(count[el.id]<2){
        res.push(el);
   }
})
 console.log(res)//[{ id: 1, name: 'kumar' },{ id: 2, name: 'kumar1' },{ id: 3, name: 'kumar2' }]enter code here

let arrayB = [
   {id: 1, name: "abc"}, 
   {id:2, name: "abccc"},
   {id: 2, name: "xyz"}, 
   {id:3, name: "abccc"},
   {id: 4, name : "asdada"}
  ];

function findRepeatedObject(arr) {
  var newObj = {};
  var newArr = [];
  for (i = 0; i < arr.length; i++) {
    if (newObj[arr[i].id]) {
      newObj[arr[i].id] += 1;
    } else {
      newObj[arr[i].id] = 1;
      newArr.push(arr[i])
    }
  }
  return newArr;
}
console.log(findRepeatedObject(arrayB));
//output will be [{ id: 1, name: 'abc' },{ id: 2, name: 'abccc' },{ id: 3, name: 'abccc' },{ id: 4, name: 'asdada' }];

let arr =[1, 2, 3, 3, 4, 5,2, 6,3,6,1];
function removeduplicate(arr) {
  let result = [],k=0,lastoccur;
  for (let i = 0;i<arr.length;i++) {
    for (let j = 0;j<arr.length;j++) {
      if (arr[i] == arr[j]) {
        lastoccur = j 
      }
    }
    if (i === lastoccur) { 
      result[k] = arr[i];
      k++;
    }
  }
  return result;
}
console.log(removeduplicate(arr));