String to Integer atoi in DSA Typescript - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to convert a digit character to its integer value.

DSA Typescript

const digit = str.charCodeAt(0) - [1];

Drag options to blanks, or click blank then click option'

A"0".charCodeAt(0)

B"1".charCodeAt(0)

C"9".charCodeAt(0)

D"a".charCodeAt(0)

Attempts:

3 left

💡 Hint

Common Mistakes

Subtracting '1' char code instead of '0'.

Using character 'a' char code which is unrelated.

Subtracting the char code of '0' from the character code of a digit gives its integer value.

2fill in blank

medium

Complete the code to skip leading whitespace characters in the string.

DSA Typescript

while (i < str.length && str[i] === [1]) { i++; }

Drag options to blanks, or click blank then click option'

A" "

B"\t"

C"\n"

D"0"

Attempts:

3 left

💡 Hint

Common Mistakes

Checking for tab '\t' instead of space.

Checking for newline '\n' which is not leading space here.

Leading spaces are skipped by checking for the space character ' '.

3fill in blank

hard

Fix the error in the condition to detect if the current character is a digit.

DSA Typescript

if (str[i] >= [1] && str[i] <= [2]) { num = num * 10 + (str.charCodeAt(i) - [3]); }

Drag options to blanks, or click blank then click option'

A"0"

B"9"

C"0".charCodeAt(0)

D"9".charCodeAt(0)

Attempts:

3 left

💡 Hint

Common Mistakes

Using char codes for comparison instead of characters.

Subtracting '9' char code instead of '0'.

Check if character is between '0' and '9' and subtract char code of '0' to get digit value.

4fill in blank

hard

Fill both blanks to correctly handle the sign of the number.

DSA Typescript

if (str[i] === [1]) { sign = -1; i++; } else if (str[i] === [2]) { sign = 1; i++; }

Drag options to blanks, or click blank then click option'

A"-"

B"+"

C"0"

D" "

Attempts:

3 left

💡 Hint

Common Mistakes

Confusing '+' and '-' characters.

Not incrementing index after sign.

Minus sign sets sign to -1, plus sign sets sign to 1 and both advance index.

5fill in blank

hard

Fill all three blanks to clamp the number within 32-bit signed integer range.

DSA Typescript

if (num * sign < [1]) return [1];
if (num * sign > [2]) return [2];
return num * sign;

Drag options to blanks, or click blank then click option'

A-2147483648

B2147483647

C0

D1

Attempts:

3 left

💡 Hint

Common Mistakes

Using 0 or 1 as clamp limits instead of 32-bit int limits.

Not clamping at all.

Clamp to minimum -2147483648 and maximum 2147483647 for 32-bit signed integer.

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