题解 | #把字符串转换成整数(atoi)#

import java.util.*;
import java.math.*;


public class Solution {
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param s string字符串 
     * @return int整型
     */
    public int StrToInt (String s) {
        s = s.trim();
        
        char[] chs = s.toCharArray();
        int flag = 1,i;
        StringBuffer ans = new StringBuffer("");
        
        i = 0;
        if(i<chs.length&&(chs[i] == '-' || chs[i] == '+')){
            if(chs[i] == '-')flag = -1;
            i++;
        }
        while(i<chs.length&&chs[i] >= '0' && chs[i] <= '9')ans.append(chs[i++]);
        
        if(ans.toString().equals(""))return 0;
        else {
            BigDecimal a = new BigDecimal(Integer.MAX_VALUE);
            BigDecimal b = new BigDecimal(ans.toString());
            if(a.compareTo(b)>=0){
                return flag*Integer.valueOf(ans.toString());
            } else {
                if(flag == 1)return Integer.MAX_VALUE;
                else return Integer.MIN_VALUE;
            }
        }
    }
}