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Solution to Sub-task: Blank Insertions

Explore how to implement a recursive JavaScript function that inserts spaces at various positions in a line. Understand base cases and recursive logic, including helper functions, to generate all unique combinations of added blanks for text manipulation tasks.

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Blank insertions

In this step, add a certain number of spaces in a line and produce all possible combinations of added spaces at different positions.

Node.js
// helper function to permute combinations of adding just one space
// input -> [String] eg. ['he', 'l', 'lo']
// Output -> [[String]] 
// eg. [ ['he', ' ', 'l', 'lo'],
//       ['he', 'l', ' ', 'lo'], ]
function singleBlankInsert(line){
  // when only two words basecase
  if(line.length === 2) return [[line[0],' ',line[1]]];
  // when only one word basecase
  if(line.length <= 1) return [line];
  let [head, ...tail] = line;
  let answer = singleBlankInsert(tail);
  answer = answer.map(x => [head, ...x]);
  answer.push([head, ' ', ...tail]);
  return answer;
}
function blankInsertions(num, line){
  if(num === 0) return [line];
  if(line.length <= 1) return [line];
  let answer = blankInsertions(num-1, line);
  // insert one blank for each line using map
  answer = answer.map(x => singleBlankInsert(x));
  // flatten the array
  answer = answer.reduce((prev, curr)=> prev.concat(curr), []);
  // filter duplicates
  return Array.from(new Set(answer.map(JSON.stringify)), JSON.parse)
}
enHyp = {
  "creative" : ["cr","ea","ti","ve"], 
  "controls" : ["co","nt","ro","ls"], 
  "achieve" : ["ach","ie","ve"], 
  "future" : ["fu","tu","re"], 
  "present" : ["pre","se","nt"], 
  "motivated" : ["mot","iv","at","ed"], 
  "desire" : ["de","si","re"], 
  "others" : ["ot","he","rs"],
}
console.log(blankInsertions( 2, ["A", "creative", "man"]))

Solve this solution recursively, where our base cases are as follows.

  • Number of spaces num that we need to add is zero (line 19)
  • Length of the line is less than or equal to one, and no spaces are added (line 20
...