String to Integer_Leetcode_#8

1.题目

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.

2.解法

思路：考虑各种不规则输入如“ +000123”，“-123abc23”， 以及溢出。

时间复杂度：O（N）

public class Solution {
public int myAtoi(String str) {
int res = 0;
int i = 0;
int sign = 1;
int digit = 0;
int max = Integer.MAX_VALUE / 10;
int len = str.length();
while(i < len && str.charAt(i) == ' '){
++i;
}
if(i == len) return 0;
if(str.charAt(i) == '-'){
++i;
sign = -1;
}else if(str.charAt(i) == '+'){
++i;
}
while(i < len && Character.isDigit(str.charAt(i))){
digit = Character.getNumericValue(str.charAt(i));
if(res > max){
return (sign == 1)? Integer.MAX_VALUE: Integer.MIN_VALUE;
}
if(res == max && digit >= 8 && sign == -1){
return Integer.MIN_VALUE;
}
if(res == max && digit >= 7 && sign == 1){
return Integer.MAX_VALUE;
}
res = res * 10 + digit;
++i;
}
return res * sign;
}
}