String——string-to-integer-atoi

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本文介绍了一种将字符串转换为整数的有效算法，并详细解释了处理各种输入情况的方法，包括空字符串、空白字符、正负号及边界值处理。

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

public class Solution {
    public int atoi(String str) {
        if(str == null||str.trim().length() == 0)
            return 0;
        str=str.trim();//考虑前后有空格的出现
        char[]ch=str.toCharArray();
        long sum=0;
        int flag=1;
        for(int i=0;i<ch.length;i++)
            {
            if(ch[i]<'0'||ch[i]>'9')
                {
                if(i == 0)
                    {
                    if(ch[i] == '+')
                        continue;
                    else if(ch[i] == '-')
                        {
                        flag=-1;
                        continue;
                    }
                    else
                        break;//"123a123"这种情况，打印123
                }
                else
                    break;
            }
            sum=sum*10+ch[i]-'0';
        }
        sum=sum*flag;
        if(sum>Integer.MAX_VALUE)
            return Integer.MAX_VALUE;
        if(sum<Integer.MIN_VALUE)
            return Integer.MIN_VALUE;
        return (int)sum;
    }
}