String to Integer atoi in DSA Javascript - Practice Problems & Challenges

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this atoi implementation for input " -42abc"?

Consider the following JavaScript function that converts a string to an integer similar to atoi. What will be printed when calling myAtoi(" -42abc")?

DSA Javascript

function myAtoi(s) {
  let i = 0, sign = 1, result = 0;
  while (s[i] === ' ') i++;
  if (s[i] === '-' || s[i] === '+') {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("  -42abc"));

A 0

B NaN

C -42

D 42

💡 Hint

Focus on how the function skips spaces, reads the sign, and stops reading digits when a non-digit appears.

The function skips leading spaces, detects the '-' sign, then reads digits '4' and '2' before stopping at 'a'. It returns -42.

❓ Predict Output

intermediate

What is the output of this atoi variant for input "+4193 with words"?

Given this JavaScript function similar to atoi, what will myAtoi("+4193 with words") print?

DSA Javascript

function myAtoi(s) {
  let i = 0, sign = 1, result = 0;
  while (s[i] === ' ') i++;
  if (s[i] === '-' || s[i] === '+') {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("+4193 with words"));

A 4193

B 0

C -4193

D NaN

💡 Hint

Check how the function handles the '+' sign and stops reading digits at the first non-digit.

The function reads the '+' sign as positive, then parses digits '4', '1', '9', '3' before stopping at space.

❓ Predict Output

advanced

What is the output of this atoi function for input "words and 987"?

What will the following JavaScript function print when called with myAtoi("words and 987")?

DSA Javascript

function myAtoi(s) {
  let i = 0, sign = 1, result = 0;
  while (s[i] === ' ') i++;
  if (s[i] === '-' || s[i] === '+') {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  if (s[i] < '0' || s[i] > '9') return 0;
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("words and 987"));

A -987

B 987

C NaN

D 0

💡 Hint

Notice the check after skipping spaces and sign that returns 0 if the next character is not a digit.

Since the first non-space character is 'w' which is not a digit or sign, the function returns 0 immediately.

❓ Predict Output

advanced

What is the output of this atoi function for input "-91283472332" considering 32-bit integer limits?

Given this JavaScript atoi function that clamps output to 32-bit signed integer range, what will myAtoi("-91283472332") print?

DSA Javascript

function myAtoi(s) {
  const INT_MAX = 2147483647;
  const INT_MIN = -2147483648;
  let i = 0, sign = 1, result = 0;
  while (s[i] === ' ') i++;
  if (s[i] === '-' || s[i] === '+') {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
    if (sign * result < INT_MIN) return INT_MIN;
    if (sign * result > INT_MAX) return INT_MAX;
  }
  return sign * result;
}
console.log(myAtoi("-91283472332"));

A -91283472332

B -2147483648

C 2147483647

D 0

💡 Hint

Check how the function clamps the result to INT_MIN and INT_MAX during parsing.

The number is less than INT_MIN, so the function returns INT_MIN (-2147483648) to clamp the value.

❓ Predict Output

expert

What is the output of this atoi function for input " +0000000000012345678"?

Analyze this JavaScript atoi function and determine what myAtoi(" +0000000000012345678") prints.

DSA Javascript

function myAtoi(s) {
  let i = 0, sign = 1, result = 0;
  while (s[i] === ' ') i++;
  if (s[i] === '-' || s[i] === '+') {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("  +0000000000012345678"));

A 12345678

B NaN

C 123456789

D 0

💡 Hint

Leading zeros do not affect the numeric value; the function accumulates digits normally.

The function skips spaces and '+' sign, then reads digits including leading zeros, resulting in 12345678.

Practice

1. What is the main purpose of the atoi function in programming?

easy

A. Check if a string contains only digits

B. Convert an integer into a string

C. Sort characters in a string alphabetically

D. Convert a string representing a number into an integer

Solution

1. Step 1: Understand the function name

   atoi stands for ASCII to integer, meaning it converts strings to integers.

2. Step 2: Identify the function's purpose

   It takes a string input and returns its integer value if possible.

3. Final Answer:

   Convert a string representing a number into an integer -> Option D

4. Quick Check:

   atoi = string to integer conversion [OK]

Hint: Remember atoi means ASCII to integer conversion [OK]

Common Mistakes:

• Confusing atoi with integer to string conversion
• Thinking atoi sorts strings
• Assuming atoi validates string digits only

2. Which of the following JavaScript code snippets correctly converts the string "123" to an integer using a method similar to atoi?

easy

A. const num = Number.toString("123");

B. const num = parseInt("123");

C. const num = "123".toString();

D. const num = "123" + 0;

Solution

1. Step 1: Identify the correct conversion method

   parseInt converts a string to an integer in JavaScript, similar to atoi.

2. Step 2: Check each option

   const num = parseInt("123"); uses parseInt correctly. const num = "123".toString(); converts string to string, no change. const num = Number.toString("123"); is invalid syntax. const num = "123" + 0; concatenates string and number, resulting in a string.

3. Final Answer:

   const num = parseInt("123"); -> Option B

4. Quick Check:

   parseInt("123") = 123 [OK]

Hint: Use parseInt() to convert string to integer [OK]

Common Mistakes:

• Using toString() which returns a string
• Trying Number.toString() incorrectly
• Adding 0 to string results in string concatenation

3. What will be the output of the following JavaScript code?

function myAtoi(str) {
  let i = 0, sign = 1, result = 0;
  while (str[i] === ' ') i++;
  if (str[i] === '-' || str[i] === '+') {
    sign = str[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < str.length && str[i] >= '0' && str[i] <= '9') {
    result = result * 10 + (str[i].charCodeAt(0) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("  -42abc"));

medium

A. 0

B. 42

C. -42

D. NaN

Solution

1. Step 1: Skip leading spaces and check sign

   The function skips spaces, finds '-', sets sign to -1, moves index forward.

2. Step 2: Convert digits until non-digit

   Reads '4' and '2', converts to number 42, stops at 'a'.

3. Step 3: Apply sign and return

   Returns -1 * 42 = -42.

4. Final Answer:

   -42 -> Option C

5. Quick Check:

   myAtoi(" -42abc") = -42 [OK]

Hint: Skip spaces, check sign, parse digits until non-digit [OK]

Common Mistakes:

• Not skipping spaces before sign
• Ignoring sign and returning positive number
• Parsing non-digit characters

4. Identify the bug in this myAtoi function implementation:

function myAtoi(str) {
  let i = 0, sign = 1, result = 0;
  while (str[i] === ' ') i++;
  if (str[i] === '-' || str[i] === '+') {
    sign = str[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < str.length && str[i] >= '0' && str[i] <= '9') {
    result = result * 10 + (str[i] - '0');
    i++;
  }
  return sign * result;
}

medium

A. Subtracting characters directly without charCodeAt causes NaN

B. Missing check for empty string input

C. Sign is not applied correctly

D. Loop does not skip spaces

Solution

1. Step 1: Analyze digit conversion

   Expression str[i] - '0' tries to subtract strings, which results in NaN in JavaScript.

2. Step 2: Correct approach

   Use str[i].charCodeAt(0) - '0'.charCodeAt(0) to get numeric value of digit character.

3. Final Answer:

   Subtracting characters directly without charCodeAt causes NaN -> Option A

4. Quick Check:

   String subtraction needs charCodeAt() [OK]

Hint: Use charCodeAt() to convert char digits to numbers [OK]

Common Mistakes:

• Subtracting characters directly causing NaN
• Not handling empty or invalid input
• Ignoring sign application

5. You want to implement myAtoi that converts a string to a 32-bit signed integer. Which approach correctly handles overflow and returns the clamped value if the number is out of range?

function myAtoi(str) {
  let i = 0, sign = 1, result = 0;
  const INT_MAX = 2147483647;
  const INT_MIN = -2147483648;
  while (str[i] === ' ') i++;
  if (str[i] === '-' || str[i] === '+') {
    sign = str[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < str.length && str[i] >= '0' && str[i] <= '9') {
    let digit = str[i].charCodeAt(0) - '0'.charCodeAt(0);
    if (result > Math.floor(INT_MAX / 10) || (result === Math.floor(INT_MAX / 10) && digit > INT_MAX % 10)) {
      return sign === 1 ? INT_MAX : INT_MIN;
    }
    result = result * 10 + digit;
    i++;
  }
  return sign * result;
}

hard

A. Correctly clamps overflow and returns 32-bit integer limits

B. Does not handle overflow, may return incorrect large numbers

C. Returns NaN on overflow instead of clamping

D. Ignores sign when clamping overflow values

Solution

1. Step 1: Check overflow condition

   The code checks if adding the next digit causes overflow by comparing with INT_MAX/10 and last digit.

2. Step 2: Return clamped value

   If overflow detected, returns INT_MAX or INT_MIN depending on sign, correctly clamping the value.

3. Step 3: Otherwise accumulate result

   Accumulates digits safely within 32-bit integer range.

4. Final Answer:

   Correctly clamps overflow and returns 32-bit integer limits -> Option A

5. Quick Check:

   Overflow check and clamp = correct behavior [OK]

Hint: Check overflow before multiply, clamp to INT_MAX/INT_MIN [OK]

Common Mistakes:

• Not checking overflow before multiplication
• Returning wrong values on overflow
• Ignoring sign when clamping