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

Challenge - 5 Problems

❓ Predict Output

intermediate

What is the output of this atoi implementation?

Given the following TypeScript code that converts a string to an integer, what will be printed when calling myAtoi(" -42abc")?

DSA Typescript

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

A -42

B NaN

C 42

D 0

💡 Hint

Focus on how the function skips spaces, checks sign, and parses digits until a non-digit.

The function skips leading spaces, detects the '-' sign, then parses digits '4' and '2' until it hits 'a' which is not a digit. So it returns -42.

❓ Predict Output

intermediate

What does this atoi variant return for input "4193 with words"?

Consider this TypeScript function that converts a string to an integer. What is the output of myAtoi("4193 with words")?

DSA Typescript

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

A 0

B 4193

C 4193 with words

D -4193

💡 Hint

The function stops parsing digits when it encounters a non-digit character.

The function parses digits '4', '1', '9', '3' and stops at the space before 'with'. It returns 4193.

🔧 Debug

advanced

What is the output of this atoi code for "+-12"?

This TypeScript function attempts to convert a string to an integer. What is the output of myAtoi("+-12")?

DSA Typescript

function myAtoi(s: string): number {
  let i = 0, sign = 1, result = 0;
  while (i < s.length && s[i] === ' ') i++;
  if (i < s.length && (s[i] === '+' || s[i] === '-')) {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  if (i < s.length && (s[i] === '+' || s[i] === '-')) {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s.charCodeAt(i) - '0'.charCodeAt(0));
    i++;
  }
  return sign * result;
}
console.log(myAtoi("+-12"));

A -12

B NaN

C SyntaxError

D 0

💡 Hint

Check how the function handles multiple signs in a row.

The function reads the first '+' as sign +1, then reads the second '-' as sign -1, then parses digits '1' and '2' for result=12. Returns -12.

🚀 Application

advanced

How many digits are parsed by this atoi call?

Using this TypeScript atoi function, how many digits are parsed when calling myAtoi("0000012345abc")?

DSA Typescript

function myAtoi(s: string): number {
  let i = 0, sign = 1, result = 0;
  while (i < s.length && s[i] === ' ') i++;
  if (i < s.length && (s[i] === '+' || s[i] === '-')) {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  let count = 0;
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    result = result * 10 + (s.charCodeAt(i) - '0'.charCodeAt(0));
    i++;
    count++;
  }
  console.log(count);
  return sign * result;
}
myAtoi("0000012345abc");

A 10

B 5

C 6

D 0

💡 Hint

Count all digits including leading zeros until first non-digit.

The function counts all digits including leading zeros: '0','0','0','0','0','1','2','3','4','5' = 10 digits.

🧠 Conceptual

expert

What is the output of this atoi with overflow handling?

This TypeScript function converts a string to a 32-bit signed integer with overflow checks. What is the output of myAtoi("9223372036854775808")?

DSA Typescript

function myAtoi(s: string): number {
  let i = 0, sign = 1, result = 0;
  const INT_MAX = 2147483647;
  const INT_MIN = -2147483648;
  while (i < s.length && s[i] === ' ') i++;
  if (i < s.length && (s[i] === '+' || s[i] === '-')) {
    sign = s[i] === '-' ? -1 : 1;
    i++;
  }
  while (i < s.length && s[i] >= '0' && s[i] <= '9') {
    const digit = s.charCodeAt(i) - '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;
}
console.log(myAtoi("9223372036854775808"));

A 0

B 9223372036854775808

C 2147483647

D -2147483648

💡 Hint

Check how the function limits the result to 32-bit integer max/min values.

The input number is larger than 32-bit max, so the function returns INT_MAX = 2147483647.

Practice

1. What does the atoi function do when given a string input?

easy

A. Converts the string to a floating-point number

B. Reverses the string characters

C. Converts the string to an integer number

D. Counts the number of characters in the string

Solution

1. Step 1: Understand the purpose of atoi

   The atoi function stands for ASCII to integer and converts a string representing a number into an integer value.

2. Step 2: Compare options with function behavior

   Only Converts the string to an integer number correctly describes this conversion. Other options describe different operations unrelated to atoi.

3. Final Answer:

   Converts the string to an integer number -> Option C

4. Quick Check:

   atoi converts string to integer [OK]

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

Common Mistakes:

• Thinking atoi converts to float
• Confusing atoi with string reversal
• Assuming atoi counts characters

2. Which of the following TypeScript function signatures correctly represents a simple atoi function?

easy

A. function atoi(str: string): number

B. function atoi(num: number): string

C. function atoi(str: number): string

D. function atoi(): void

Solution

1. Step 1: Identify input and output types for atoi

   atoi takes a string input and returns a number (integer).

2. Step 2: Match function signature with correct types

   function atoi(str: string): number matches this: input is string, output is number. Other options have wrong input/output types or no parameters.

3. Final Answer:

   function atoi(str: string): number -> Option A

4. Quick Check:

   Input string, output number [OK]

Hint: atoi input is string, output is number [OK]

Common Mistakes:

• Swapping input and output types
• Using no parameters
• Using wrong parameter types

3. What is the output of the following TypeScript code?

function atoi(str: string): number {
  let i = 0, num = 0, sign = 1;
  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') {
    num = num * 10 + (str.charCodeAt(i) - 48);
    i++;
  }
  return num * sign;
}
console.log(atoi("  -42abc"));

medium

A. -42

B. 42

C. 0

D. NaN

Solution

1. Step 1: Skip leading spaces and detect sign

   The code skips spaces, finds '-', so sign = -1, index moves past '-'.

2. Step 2: Parse digits until non-digit

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

3. Step 3: Apply sign and return

   Returns 42 * -1 = -42.

4. Final Answer:

   -42 -> Option A

5. Quick Check:

   Parsed number with sign = -42 [OK]

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

Common Mistakes:

• Not skipping spaces
• Ignoring sign character
• Parsing non-digit characters

4. The following TypeScript atoi implementation has a bug. What is the bug?

function atoi(str: string): number {
  let num = 0;
  let i = 0;
  while (i < str.length && str[i] === ' ') i++;
  for (; i < str.length; i++) {
    if (str[i] < '0' || str[i] > '9') break;
    num = num * 10 + (str.charCodeAt(i) - 48);
  }
  return num;
}

medium

A. Returns string instead of number

B. Does not handle leading spaces

C. Does not stop parsing at non-digit characters

D. Does not handle negative or positive signs

Solution

1. Step 1: Check for sign handling

   The code does not check for '+' or '-' signs before parsing digits.

2. Step 2: Verify other behaviors

   It skips leading spaces, stops parsing at first non-digit and returns number, so no issue there. The main bug is missing sign handling.

3. Final Answer:

   Does not handle negative or positive signs -> Option D

4. Quick Check:

   Missing sign handling in atoi [OK]

Hint: Check if signs '+' or '-' are handled [OK]

Common Mistakes:

• Assuming spaces are main bug
• Thinking it parses non-digit characters
• Confusing return type

5. You want to extend the atoi function to handle integer overflow by clamping the result between INT_MIN = -2147483648 and INT_MAX = 2147483647. Which code snippet correctly clamps the value before returning?

const INT_MIN = -2147483648;
const INT_MAX = 2147483647;

function atoi(str: string): number {
  let i = 0, num = 0, sign = 1;
  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') {
    num = num * 10 + (str.charCodeAt(i) - 48);
    i++;
  }
  num = num * sign;
  // Clamp here
  // ???
  return num;
}

hard

A. if (num > INT_MIN) return INT_MIN; if (num < INT_MAX) return INT_MAX;

B. if (num < INT_MIN) return INT_MIN; if (num > INT_MAX) return INT_MAX;

C. if (num < INT_MAX) return INT_MIN; if (num > INT_MIN) return INT_MAX;

D. if (num === INT_MIN) return INT_MAX; if (num === INT_MAX) return INT_MIN;

Solution

1. Step 1: Understand clamping logic

   If number is less than INT_MIN, return INT_MIN; if greater than INT_MAX, return INT_MAX.

2. Step 2: Match correct condition and return

   if (num < INT_MIN) return INT_MIN; if (num > INT_MAX) return INT_MAX; correctly checks and returns clamped values. Other options have incorrect comparisons or swap min/max.

3. Final Answer:

   if (num < INT_MIN) return INT_MIN; if (num > INT_MAX) return INT_MAX; -> Option B

4. Quick Check:

   Clamp below min and above max correctly [OK]

Hint: Clamp with if less than min or greater than max [OK]

Common Mistakes:

• Swapping INT_MIN and INT_MAX in conditions
• Using equality instead of inequality
• Returning wrong clamp value