题解 | #把字符串转换成整数(atoi)#

各种标识一点一点做出来的

import java.util.*;


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) {
        // write code here
        int ret = 0;
        int flag = 1;
        char[] chs = s.toCharArray();
        
        int isFlag = 0;
        int isNum = 0;
        
        for(int i=0;i<chs.length;++i){
            if(chs[i] == ' '){
                if(isNum == 1) break;
                if(isFlag == 1) break;
                continue;
            }
            if((chs[i] >'9' || chs[i]<'0') && chs[i]!='-' 
               && chs[i]!='+') break;
            
            if(chs[i] == '-'){
                if(isNum == 1) break;
                if(isFlag == 1) break;
                isFlag = 1;
                
                if(flag == -1) break;
                flag = -1;
                continue;
            }
            if(chs[i] == '+'){
                if(isNum == 1) break;
                isFlag = 1;
                if(flag == -1) break;
                flag = 1;
                continue;
            }
            
            int n = chs[i] - '0';
            if(flag == 1 && ret > (Integer.MAX_VALUE-n)/10){
                ret = Integer.MAX_VALUE;
                break;
            }
            if(flag == -1 && -ret < (Integer.MIN_VALUE+n)/10){
                ret = Integer.MIN_VALUE;
                break;
            }
            ret = ret * 10 + n;
            isNum = 1;
        }
        return flag * ret;
    }
}