Remove all adjacent repeating characters from input

Question

The function unique_in_order which takes as argument a sequence and returns a list of items without any elements with the same value next to each other and preserving the original order of elements.

For example:

uniqueInOrder('AAAABBBCCDAABBB') == ['A', 'B', 'C', 'D', 'A', 'B'] 
uniqueInOrder('ABBCcAD') == ['A', 'B', 'C', 'c', 'A', 'D'] 
uniqueInOrder([1,2,2,3,3]) == [1,2,3]

Answer 1

What you want to do first is normalize your input such that whether it's a string or an array, it doesn't matter.

const input = Array.isArray(x) ? x : x.split('');

After the above, the input will always be an array. Now the logic for skipping is duplicates is quite simple

for (let i = 0; i < input.length; ++i) {
  if (input[i] == input[i + 1]) continue
  result.push(input[i])
}

You continue, i.e. skip each index in the input that is the same as the next for each index. Then for each element that isn't duplicated, you push into your result array.

The whole thing looks like this:

function uniqueInOrder(x) {
  const result = [];
  const input = Array.isArray(x) ? x : x.split('');

  for (let i = 0; i < input.length; ++i) {
    if (input[i] == input[i + 1]) continue
    result.push(input[i])
  }
  
  return result
}

console.log(uniqueInOrder('AAAABBBCCDAABBB'));
console.log(uniqueInOrder('ABBCcAD'));
console.log(uniqueInOrder([1, 2, 2, 3, 3]));

If you're familiar with the filter function you can make it a one liner.

function uniqueInOrder(x) {
  return (Array.isArray(x) ? x : x.split(''))
    .filter((c, i) => c !== x[i + 1]);
}

console.log(uniqueInOrder('AAAABBBCCDAABBB'));
console.log(uniqueInOrder('ABBCcAD'));
console.log(uniqueInOrder([1, 2, 2, 3, 3]));

Answer 2

Offered is two different solutions, depending on what you want:

1. You can use Set() for unique sets. Simply adding the value to a set will retain the order and prevent unique values from being added.

2. For contiguously unique sets, you can use filter to iterate over an array.

   • If the argument is a string, this array is created by splitting on a blank string (.split(''))
   • When iterating over the array of input values, you can compare the current value to the previous; if they are different then return true
   • A true response will include the value in the array you will be creating as a result of the filter (which holds your unique values)

uniqueInOrder('AAAABBBCCDAABBB') == ['A', 'B', 'C', 'D', 'A', 'B']
uniqueInOrder('ABBCcAD') == ['A', 'B', 'C', 'c', 'A', 'D']
uniqueInOrder([1, 2, 2, 3, 3]) == [1, 2, 3]



function unique(input) {
  var set = new Set(),
    arr = input;
    
  if (typeof input == 'string')
    arr = arr.split('');

  arr.forEach(val => {
    set.add(val)
  });

  console.log('input:',input);
  console.log('unique:',[...set]);
  return [...set];
}

function uniqueInOrder(input) {
  var arr = input;
  if (typeof input == 'string')
    arr = arr.split('');

  var unique = arr.filter((val,i,arr)=>{
    return val !== arr[i-1];
  });

  console.log('input:', JSON.stringify(input));
  console.log('uniqueInOrder:', JSON.stringify(unique));
  return unique;
}