008 String to Integer (atoi) 字符串转换为整数

详见：https://leetcode.com/problems/string-to-integer-atoi/description/

实现语言：Java

class Solution {
    public int myAtoi(String str) {
        int index =0;
        Long total = new Long(0);
        int sign = 1;
        while(index < str.length()  && str.charAt(index) == ' '){
            ++index;
        }

        if(index == str.length()){
            return (int)(total*sign);
        }

        if(str.charAt(index) == '-' || str.charAt(index) == '+'){
            sign = str.charAt(index) == '-'?-1 : 1;
            index++;
        }

        while(index < str.length() && str.charAt(index) >= '0' && str.charAt(index) <= '9'){
            total = total *10 + str.charAt(index) - '0';
            ++index;
        
            if(total > Integer.MAX_VALUE){
                return sign==1?Integer.MAX_VALUE:Integer.MIN_VALUE;
            }
        }
        return (int)(total*sign);
    }
}

 实现语言：C++

class Solution {
public:
    int myAtoi(string str) {
        int n=str.size();
        if(n==0||str.empty())
        {
            return 0;
        }
        int sign=1,base=0,i=0;
        while(i<n&&str[i]==' ')
        {
            ++i;
        }   
        if(str[i]=='+'||str[i]=='-')
        {
            sign=str[i++]=='+'?1:-1;
        }
        while(i<n&&str[i]>='0'&&str[i]<='9')
        {
            if(base>INT_MAX/10||(base==INT_MAX/10&&str[i]-'0'>7))
                return sign==1?INT_MAX:INT_MIN;
            base=base*10+str[i++]-'0';
        }
        return sign*base;
    }
};

 参考：http://www.cnblogs.com/grandyang/p/4125537.html