Category: interview

Multi List Iterator – Javascript

Post author By Shiva Charan Devabhaktuni
Post date May 10, 2021

Print a list of lists vertically using an Iterator.

For example:

// Usage
const node = new MultiIterator([[1, 2], [], [4], [5]]);

while (node.hasNext()) {
  console.log(node.next());
}

Input:

[[1, 2], [], [4], [5]]

Output:

class MultiIterator {
  constructor(inp) {
    this.inp = inp;
    this.x = -1;
    this.inpLen = inp.length;
    this.levelProgress = Array(inp.length).fill(0);
    this.nextX = 0;
  }

  hasNext() {
    var count = 0;
    var listIndex = this.x;
    var elemIndex;
    do {
      listIndex++;
      listIndex %= this.inpLen;
      elemIndex = this.levelProgress[listIndex]; // index = size - 1
      count++;
    } while (count < this.inpLen && elemIndex === this.inp[listIndex].length)
    if (elemIndex === this.inp[listIndex].length) {
      return false;
    }
    this.nextX = listIndex;
    return true;
  }

  next() {
    if (this.hasNext()) {
      this.x = this.nextX;
      this.levelProgress[this.x]++;
      return this.inp[this.x][this.levelProgress[this.x] - 1];
    }
    return null;
  }
}

// Test Code
const node = new MultiIterator([
  [1, 2],
  [],
  [4],
  [5],
]);

while (node.hasNext()) {
  console.log(node.next());
}

Demo

You can print this list horizontally as well.

For example:

Input:

[[1, 2], [], [4], [5]]

Output:

class MultiIterator {
  constructor(inp) {
    this.inp = inp;
    this.x = 0;
    this.y = -1;
    this.inpLen = inp.length;
    this.nextX = 0;
    this.nextY = 0;
  }

  hasNext() {
    var listIndex = this.x;
    var elemIndex = this.y + 1;
    while (listIndex < this.inpLen && elemIndex === this.inp[listIndex].length) {
      listIndex++;
      elemIndex = 0;
    }
    if (listIndex === this.inpLen) {
      return false;
    }
    this.nextX = listIndex;
    this.nextY = elemIndex;
    return true;
  }

  next() {
    if (this.hasNext()) {
      this.x = this.nextX;
      this.y = this.nextY;
      return this.inp[this.nextX][this.nextY];
    }
    return null;
  }
}

// Test Code
const node = new MultiIterator([
  [1, 2],
  [],
  [4],
  [5],
]);

while (node.hasNext()) {
  console.log(node.next());
}

Demo

Tags es6, facebook, google, js, question, solution, working

interview

Items in Container

Post author By Shiva Charan Devabhaktuni
Post date May 7, 2021

const getItems = (str, startIndices, endIndices) => {
  let count = 0;
  const arr = Array(str.length);
  arr[0] = 0;
  for (let i = 1; i < str.length; i++) {
    if (str[i] === '*') {
      count++;
      arr[i] = arr[i - 1];
    } else {
      arr[i] = count;
    }
  }
  const ret = Array(startIndices.length);
  for (let i = 0; i < startIndices.length; i++) {
    ret[i] = arr[endIndices[i] - 1] - arr[startIndices[i] - 1];
  }
  return ret;
}

console.log(getItems('|**|*|*', [1, 1], [5, 6])); // [2,3]

Demo

Tags 105, 2021, amazon, amcat, assessment, es6, interview, javascript, mins, online, sde1, SDE2, SDE3, sdeI, SDEII, SDEIII

interview

In-Flight Media

Post author By Shiva Charan Devabhaktuni
Post date May 7, 2021

// In-Flight Media

const getMovies = (flightDuration, movieDurations) => {
  const movieTargetDuration = flightDuration - 30;
  const requiredDurations = {};
  var ret = [];
  for (let [key, movieDuration] of Object.entries(movieDurations)) {
    if (movieDuration in requiredDurations) {
      // Found a pair.
      ret.push([requiredDurations[movieDuration], parseInt(key)]);
    }
    requiredDurations[movieTargetDuration - movieDuration] = parseInt(key);
  }

  // Find the pair with the maximum duration movie.
  var maxDuration = -1;
  var maxLoc = -1;
  for (let [key, value] of Object.entries(ret)) {
    var currMax = Math.max(movieDurations[value[0]], movieDurations[value[1]]);
    if (currMax > maxDuration) {
      maxDuration = currMax;
      maxLoc = key;
    }
  }
 
  // If no pair found then return [-1, 1].
  return maxLoc > -1 ? ret[maxLoc] : [-1, 1];
};

console.log(getMovies(90, [1, 10, 25, 35, 60])); // [2,3]

Demo

Tags 105, amazon, amcat, coding assessment, es6, javascript, mins, online, sde1, SDE2, SDE3, sdeI, SDEII, SDEIII, submission, timed

interview

Implement Array.prototype.map()

Post author By Shiva Charan Devabhaktuni
Post date May 4, 2021

Array.prototype.map = function(mapper, thisArg) {
  const arr = [];

  for (const [key] of Object.entries(this)) {
    arr[key] = mapper.call(thisArg, this[key], key >>> 0, this);
  }

  return arr;
}

const arr = [];
arr[0] = 0;
arr[2] = 2;
arr[3] = 3;
console.log(arr); // [0, undefined, 2, 3]
console.log(arr.map(x => 2 * x)); // [0, undefined, 4, 6]

Demo

interview

Create Array of size in Js

Post author By Shiva Charan Devabhaktuni
Post date May 2, 2021

const arr = Array(3).fill(5);
console.log(arr); // [5, 5, 5]

Demo

interview

Uglify CSS Class names

Post author By Shiva Charan Devabhaktuni
Post date May 2, 2021



/**
 * @returns {string}
 */
function getUniqueClassName() {
  getUniqueClassName.count = getUniqueClassName.count || 1;

  var helper = () => {
    var count = getUniqueClassName.count++;
    var ret = '';
    while (count > 0) {
      var curr = (count - 1) % 52;
      ret = String.fromCharCode((curr < 26) ? 97 /* a */ + curr : 65      /* A */ + (curr - 26)) + ret;
      count = Math.floor((count - 1) / 52);
    }
    return ret;
  }

  return helper();
}

getUniqueClassName.reset = function() {
  getUniqueClassName.count = 0;
}

console.log(getUniqueClassName()); // a
console.log(getUniqueClassName()); // b

Demo

interview

HTMLElement to Virtual DOM and back

Post author By Shiva Charan Devabhaktuni
Post date April 28, 2021

/**
 * @param {HTMLElement} 
 * @return {object} object literal presentation
 */
function virtualize(element) {
  if (element.nodeType === 3)
    return element.textContent;
  const ret = {
    type: element.tagName.toLowerCase(),
    props: {
      children: []
    }
  };
  element.childNodes.forEach(child => ret.props.children.push(virtualize(child)));
  if (ret.props.children.length === 1)
    ret.props.children = ret.props.children[0];
  for (const {
      name,
      value
    } of element.attributes)
    ret.props[name === 'class' ? 'className' : name] = value;
  return ret;
}

/**
 * @param {object} valid object literal presentation
 * @return {HTMLElement} 
 */
function render(obj) {
  if (typeof obj === 'string') return document.createTextNode(obj);
  const {
    type,
    props: {
      children,
      ...attributes
    }
  } = obj;
  const ret = document.createElement(type);
  const childNodes = typeof children === 'string' ? [children] : children;
  childNodes.forEach(childNode => ret.append(render(childNode)));
  for (const [key, val] of Object.entries(attributes)) {
    ret.setAttribute(key === 'className' ? 'class' : key, val)
  }
  return ret;
}

Demo

Tags deserialize, DOM, facebook, front end, interview, javascript, js, meta, react, serialize, vanilla

interview

Is Element in View

Post author By Shiva Charan Devabhaktuni
Post date April 27, 2021

<body onscroll="onscroll()">

  <div style="width: 400px; height:800px; border:1px solid #222;">Scroll Down</div>

  <div id="demo">
    Demo
  </div>

</body>

const isInView = (element) => {
  const {
    top,
    right,
    bottom,
    left
  } = element.getBoundingClientRect();

  return top >= 0 &&
    left >= 0 &&
    right <= (window.innerWidth || document.documentElement.clientWidth) &&
    bottom <= (window.innerHeight || document.documentElemetn.clientHeight);
};

const demo = document.getElementById('demo');

const onscroll = function() {
  console.log(isInView(demo));
};

Demo

Tags es6, js, script, scroll

interview

accessKey

Post author By Shiva Charan Devabhaktuni
Post date April 25, 2021

<div>Test</div>

const demo = document.getElementById('demo');

 demo.onclick = (e) => {
   console.log(e.target.textContent);
 };
 demo.accessKey = 'w';

 // Alt + W for Windows + Chrome
 // [Control] [Option] + accesskey for Mac
 // Alt + W for Linux + Chrome

Demo

Tags es6, js

interview

Staircase using repeat()

Post author By Bharat Mandava
Post date April 25, 2021

Runtime Complexity: O(n^2)

/*Create a staircase based on user input n.

steps(5) should return the below output:
"#    "
"##   "
"###  "
"#### "
"#####" 
*/

const steps = (n) => {
if( n > 0){
  for (let row = 0; row < n; row++) {
      let step = '';

      for (let col = 0; col < n; col++) {
        col <= row ? step += '#' : step += ' ';
      }
       console.log(step);
   }
   return
}
console.log(`please give a number greater than 0`)
}

steps(5);
/* Output
"#    "
"##   "
"###  "
"#### "
"#####" */

Demo

String.prototype.repeat()

Introduced in ES2015+, the repeat() method constructs and returns a new string which contains the specified number of copies of the string on which it was called, concatenated together.

Syntax: str.repeat(count)
count is an integer between 0 and infinity(positive) indicating the number of times to repeat the string.

Code	Output
‘abc’.repeat(-1)	RangeError
‘abc’.repeat(0)	”
‘abc’.repeat(1)	‘abc’
‘abc’.repeat(2)	‘abcabc’
‘abc’.repeat(3.5)	‘abcabcabc’ // Uses floor
‘abc’.repeat(1/0)	Range Error

Note: If the total length of the string to be returned equals or exceeds (1 << 28, i.e., 2^28) then, this method throws a RangeError as most modern browsers can’t handle strings longer than that.

if((str.length * count) >= 1 << 28) // This

/* A simplified solution using String.prototype.repeat
 */
 
 const steps = (n) => {
  for(let i = 1; i <= n; i++) {
    let step = '#'.repeat(i) + ' '.repeat(n-i);
    console.log(step);
  }
}

steps(5);
/* Output
"#    "
"##   "
"###  "
"#### "
"#####" */

Demo

Tags es6+, interview, javascript, prototype, staircase, stairs, string methods