# 8 String to Integer (atoi) – Easy

### Problem:

Implement atoi to convert a string to an integer.

Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

### Thoughts:

The tricky part for this problem is how to handle overflow. The annoying thing here is the special cases. “010” -> 10 “+-2″ -> 0 ” 010″ -> 10 “-012ab1234” -> -12 “2147483648” -> “2147483647” “-2147483648” -> – 2147483648 Although I would think for some of these special cases we should throw Exceptions instead of returning things.

### Solutions:

``````public class Solution {
public int myAtoi(String str) {
str = str.trim();
int result = 0;
int flag = 1;
int start = 0;
if (str == null || str.length() == 0){
return 0;
}
if (str.charAt(0) == '-'){
flag = -1;
start = 1;
}
else if (str.charAt(0) == '+'){
start = 1;
}
for (int i = start; i < str.length(); i ++){
if (str.charAt(i) != '0'){
start = i;
break;
}
}
for (int i = start; i < str.length(); i ++){
char c = str.charAt(i);
if (c < 48 || c > 57){
break;
}
int digit = c - 48;
int tmp = result * 10 + digit;
if (tmp == Integer.MIN_VALUE && i == (str.length() -1) && str.charAt(0) == '-'){
return Integer.MIN_VALUE;
}
else if ((tmp - digit) / 10 != result || (result > 0 && tmp < 0)){
//overflow
if (str.charAt(0) == '-'){
return Integer.MIN_VALUE;
}
else{
return Integer.MAX_VALUE;
}
}
else{
result = tmp;
}
}
return result * flag;
}
}
``````

Updated: 10/17/2016

``````public class Solution {
public int myAtoi(String str) {
str = str.trim();
if (str.length() == 0){
return 0;
}
int i = 0, flag = 1, plus = 0, minus = 0;
long result = 0;
if (str.charAt(0) == '-') {
flag = -1;
i = 1;
}
else if (str.charAt(0) == '+') {
i = 1;
}
while (i < str.length()) {
if (str.charAt(i) >= '0' && str.charAt(i) <= '9') {
int digit = str.charAt(i) - '0';
result = result * 10 + digit;
if (result > Integer.MAX_VALUE) {
break;
}
}
else {
break;
}
i ++;
}
if (result*flag > Integer.MAX_VALUE) {
return Integer.MAX_VALUE;
}
if (result*flag < Integer.MIN_VALUE) {
return Integer.MIN_VALUE;
}
return (int) result*flag;
}
}
``````