LeetCode – String to Integer (atoi) (Java)

 

Implement atoi to convert a string to an integer.

Hint: Carefully consider all possible input cases. If you want a challenge, please do not see below and ask yourself what are the possible input cases.

Analysis

The following cases should be considered for this problem:

1. null or empty string
2. white spaces
3. +/- sign
4. calculate real value
5. handle min & max

Java Solution

public int atoi(String str) {
	if (str == null || str.length() < 1)
		return 0;
 
	// trim white spaces
	str = str.trim();
 
	char flag = '+';
 
	// check negative or positive
	int i = 0;
	if (str.charAt(0) == '-') {
		flag = '-';
		i++;
	} else if (str.charAt(0) == '+') {
		i++;
	}
	// use double to store result
	double result = 0;
 
	// calculate value
	while (str.length() > i && str.charAt(i) >= '0' && str.charAt(i) <= '9') {
		result = result * 10 + (str.charAt(i) - '0');
		i++;
	}
 
	if (flag == '-')
		result = -result;
 
	// handle max and min
	if (result > Integer.MAX_VALUE)
		return Integer.MAX_VALUE;
 
	if (result < Integer.MIN_VALUE)
		return Integer.MIN_VALUE;
 
	return (int) result;
}

Related posts:

  1. LeetCode – Length of Last Word (Java)
  2. LeetCode – Longest Substring Without Repeating Characters (Java)
  3. LeetCode – Divide Two Integers (Java)
  4. LeetCode – Integer Break (Java)
Category >> Algorithms  
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  • Bonsai

    Integer has range [-2147483648 , 2147483647] in Java. If the number is -214748364, the algorithm processes it as a positive integer and then change sign. The number would exceed the integer range if an integer is used.

  • KARAN VERMA

    One minor modification for prevent stackoverflowException: length check for string if(str.length()>0) {

    if (str == null || str.length() 0) {

    if (str.charAt(0) == '-') {

    flag = '-';

    i++;

    } else if (str.charAt(0) == '+') {

    i++;

    }

    }

    // use double to store result

    double result = 0;

    // calculate value

    while (str.length() > i && str.charAt(i) >= '0' && str.charAt(i) Integer.MAX_VALUE)

    return Integer.MAX_VALUE;

    if (result < Integer.MIN_VALUE)

    return Integer.MIN_VALUE;

    return (int) result;

  • Npy

    in next iteration when we add new integer it should come at unit’s place.

  • kavya tg

    Hi article is nice, can we parsing String to int in java 8 ?
    i was searching for the information then i found very good information here, it best way to convert string to int i hope this may be use full.

  • Ahmed Saad

    this is my solution to convert any string to double including fractions and + – signs


    private static double checkString(String text) {

    boolean isFraction = false;
    int fractionIndex = -1;
    boolean isSigned = false;
    boolean isPostive = true;

    if (text.charAt(0) == '+') {
    isSigned = true;
    isPostive = true;
    } else if (text.charAt(0) == '-') {
    isSigned = true;
    isPostive = false;
    }

    for (int i = 0; i 57 || currentChar < 48)) {
    return -1;
    }

    }

    int start = (isSigned) ? 1 : 0;
    double num;
    if (!isFraction) {
    return getNumber(text, start, text.length() - 1, false);
    } else {
    if (fractionIndex - start = start; i--) {
    char currentChar = text.charAt(i);
    num = num + level * (currentChar - 48);
    level = level * 10;
    }
    if (isFraction) {
    num = num / (level);
    }

    return num;
    }

  • Brenda Martis

    Why was double used for result?

  • Brandon Donnelson

    Alternative solution.


    public int myAtoi(String str) {
    if (str == null || str.isEmpty()) {
    return 0;
    }

    str = str.trim();

    if (str.equals("-")) {
    return 0;
    }

    if (str.equals("+")) {
    return 0;
    }

    int signAdd = 0;
    boolean sign = false;
    long result = 0;
    for (int i = 0; i 1) {
    return 0;
    }
    }

    if (c == '-') {
    sign = true;
    } else if (c == '+') {
    sign = false;
    } else if (c >= '0' && c Integer.MAX_VALUE) {
    return Integer.MAX_VALUE;
    } else if (sign && result *-1 < Integer.MIN_VALUE) {
    return Integer.MIN_VALUE;
    }

    }

    if (sign) {
    result *= -1;
    }

    return (int) result;
    }

  • Sékine Coulibaly

    I guess it mean for positive numbers, eg. 42.
    Obviously 42 is positive, and equals to +42, but there is no leading “+” sign.

  • loyolakarl

    kj;ljdaLJD

    I am writing some code as said before lol. :)

  • Rory

    Do not need this part

    // handle max and min

    if (result > Integer.MAX_VALUE)

    return Integer.MAX_VALUE;

    if (result < Integer.MIN_VALUE)

    return Integer.MIN_VALUE;

  • Renzo

    Solution in 11 lines of Python:https://github.com/renzon/code_interview_training/blob/master/string_to_int.py
    The good thing is that for integer I don’t have to worry once they are arbitrary large in Python (not arbitrary, but as long as it fit in your memory)

  • joseph

    Really should check the string length after doing the trim(), in case it was a string of just white spaces.

  • Peng

    I think the overflow check should be placed within for loop to attach this problem

  • Arnaud Hebert

    Why are we multiplying by 10: result = result * 10 ?

  • lily

    well,if the str is very very very big,such as it is bigger than long,how can you handle this?

  • he could use :
    Character.getNumericValue(str.charAt(i))

  • Chris

    Why the sign is not always supposed to be at the beginning of the string? Please give a example? Thank you.

  • sebastian

    hi is doing that because charAt return a char so you can’t sum a char, you need a way to convert to integer one choice is that and only is charAt(pos) – 48

    Bye.

  • armandm

    why are you substracting ” to the char
    ?

  • uee

    The sign is not always supposed to be at the beginning of the string. And you also didn’t consider the situation that other character show in the string.