I can't figure out why my JavaScript recursion function isn't correctly counting the number of lines, words, and characters in a text

Question

I can't figure out why my JavaScript recursion function isn't correctly counting the number of lines, words, and characters in a text

Seeking assistance with my JavaScript recursion program that is not functioning as expected. The goal is to extract words from a text file and output the count of words, lines, and characters. I am uncertain where my mistake lies, so any guidance on code modification would be greatly appreciated. Below is the JavaScript code in question:

var fs = require("fs");
var text = fs.readFileSync("text.txt", "utf8");
function countLines(text) {
  if (text == "") {
    return 0;
  } else {
    return 1 + countLines(text.substring(text.indexOf("\n") + 1));
  }
}
function countWords(text) {
  if (text == "") {
    return 0;
  } else {
    return 1 + countWords(text.substring(text.indexOf(" ") + 1));
  }
}
function countCharacters(text) {
  if (text == "") {
    return 0;
  } else {
    return 1 + countCharacters(text.substring(1));
  }
}
var lineCount = countLines(text);
var wordCount = countWords(text);
var characterCount = countCharacters(text);
console.log(
  "There are " +
    lineCount +
    " lines, " +
    wordCount +
    " words, and " +
    characterCount +
    " characters in the file."
);

Below is the content of the text.txt file:

I was running to the zoo.

javascript recursion

Answer 1

Answer №1

When it comes to counting lines, the key condition is not checking for an empty string with if (text == ""), but rather determining if there is no \n present in the text. By adjusting the base case, we open up new perspectives on the issue and streamline our code.

Assuming i represents the position of \n in the string text -

If i is negative, then text constitutes the final line. In this scenario, the function should return 1.
(inductive) If i is 0 or greater, it implies that text encompasses multiple lines. In such cases, the function should return 1 plus the outcome of the sub-problem.

function countLines(text) {
  const i = text.indexOf("\n")
  if (i < 0) return 1                                // 1
  else return 1 + countLines(text.substring(i + 1))  // 2
}

console.log(countLines(`Hello`))

console.log(countLines(`Hello
World,`))

console.log(countLines(`Hello
World,
We don't deserve you.`))

An alternative approach is to use a ternary expression for a more concise implementation -

function countLines(text) {
  const i = text.indexOf("\n")
  return (i < 0) ? 1 : 1 + countLines(text.substring(i + 1))
}

Answer 2

When it comes to counting lines, the key condition is not checking for an empty string with if (text == ""), but rather determining if there is no \n present in the text. By adjusting the base case, we open up new perspectives on the issue and streamline our code.

Assuming i represents the position of \n in the string text -

If i is negative, then text constitutes the final line. In this scenario, the function should return 1.
(inductive) If i is 0 or greater, it implies that text encompasses multiple lines. In such cases, the function should return 1 plus the outcome of the sub-problem.

function countLines(text) {
  const i = text.indexOf("\n")
  if (i < 0) return 1                                // 1
  else return 1 + countLines(text.substring(i + 1))  // 2
}

console.log(countLines(`Hello`))

console.log(countLines(`Hello
World,`))

console.log(countLines(`Hello
World,
We don't deserve you.`))

An alternative approach is to use a ternary expression for a more concise implementation -

function countLines(text) {
  const i = text.indexOf("\n")
  return (i < 0) ? 1 : 1 + countLines(text.substring(i + 1))
}

Answer 3

Answer №2

Your problem arises from a blind recursion that does not check the result of indexOf, which returns -1 if the target is not found

thus

text.substring(text.indexOf(" ") + 1)

turns into

text.substring(-1 + 1)

which is equivalent to

text.substring(0)

This results in infinite recursion for the last word (and line)

If .indexOf returns -1, you should return 1

Note: I have removed the unnecessary else in the code - absence of else when the if returns a value leads to cleaner code (although you can use else if needed

I have demonstrated two approaches to test indexOf

var text = "I was running to the zoo.";

function countLines(text) {
  if (text == "") {
    return 0;
  }
  const index = text.indexOf("\n");
  if (index  < 0) {
    return 1;
  }
  return 1 + countLines(text.substring(index + 1));
}

function countWords(text) {
  if (text == "") {
    return 0;
  }
  const index = text.indexOf(" ") + 1;
  if (index) { // since we've added 1, a "not found" -1 would be 0 here, and be falsey
    return 1 + countWords(text.substring(index));
  }
  return 1;
}

function countCharacters(text) {
  if (text == "") {
    return 0;
  } 
  return 1 + countCharacters(text.substring(1));
}
var lineCount = countLines(text);
var wordCount = countWords(text);
var characterCount = countCharacters(text);
console.log(
  "There are " +
  lineCount +
  " lines, " +
  wordCount +
  " words, and " +
  characterCount +
  " characters in the file."
);

Answer 4

Your problem arises from a blind recursion that does not check the result of indexOf, which returns -1 if the target is not found

thus

text.substring(text.indexOf(" ") + 1)

turns into

text.substring(-1 + 1)

which is equivalent to

text.substring(0)

This results in infinite recursion for the last word (and line)

If .indexOf returns -1, you should return 1

Note: I have removed the unnecessary else in the code - absence of else when the if returns a value leads to cleaner code (although you can use else if needed

I have demonstrated two approaches to test indexOf

var text = "I was running to the zoo.";

function countLines(text) {
  if (text == "") {
    return 0;
  }
  const index = text.indexOf("\n");
  if (index  < 0) {
    return 1;
  }
  return 1 + countLines(text.substring(index + 1));
}

function countWords(text) {
  if (text == "") {
    return 0;
  }
  const index = text.indexOf(" ") + 1;
  if (index) { // since we've added 1, a "not found" -1 would be 0 here, and be falsey
    return 1 + countWords(text.substring(index));
  }
  return 1;
}

function countCharacters(text) {
  if (text == "") {
    return 0;
  } 
  return 1 + countCharacters(text.substring(1));
}
var lineCount = countLines(text);
var wordCount = countWords(text);
var characterCount = countCharacters(text);
console.log(
  "There are " +
  lineCount +
  " lines, " +
  wordCount +
  " words, and " +
  characterCount +
  " characters in the file."
);

I can't figure out why my JavaScript recursion function isn't correctly counting the number of lines, words, and characters in a text

Answer №1

Answer №2

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