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Challenge Algo #5 - Almost Increasing Sequence

Farid, 34 years old, Freelancer, Full Stack Developer, Geek/n3rd and Teacher.
・1 min read

Given a sequence of integer as an array, determine whether it is possible to obtain a strictly increasing sequence removing no more than one element from the array.


  • For sequence = [1, 3, 2, 1], the output should be almostIncreasingSequence(sequence) = false;

there is no one element in this array that can be removed in order to get a strictly increasing sequence.

  • For sequence = [1, 3, 2], the output should be almostIncreasingSequence(sequence) = true;

You can remove 3 from the array to get strictly increasing sequence [1, 2]. Alternatively, you can remove 2 to get the strictly increasing sequence [1, 3].

Here we code:

const almostIncreasingSequence = sequence =>{
  // element to remove to have increasing sequence
  let count = 0;

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

    // check 1 : n is smaller or equal to n-1
    if(sequence[i] <= sequence[i-1]){
      // n is smaller or equal to n-2 and n+1 is smaller or equal to n-1
      if(sequence[i] <= sequence[i-2] && sequence[i+1] <= sequence[i-1]){

  // return true with 1 or no remove, otherwise false
  return count <= 1;

console.log(almostIncreasingSequence([1,3,2,1])); // false
console.log(almostIncreasingSequence([1,3,2])); // true
console.log(almostIncreasingSequence([3,2,1])); // false
console.log(almostIncreasingSequence([1,2,3,2])); // true
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as usually better way or more efficient are welcome in comments...

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