NC100 把字符串转换成整数(atoi)

落日映苍穹つ 2024-03-27 16:39 0阅读 0赞

> [牛客华为机试题库【题号 HJ开头】（重点看）][HJ]  
> [牛客在线编程算法篇【题号NC开头】][NC]  
> [剑指offer【题号 JZ开头】][offer_ JZ]  
> [力扣][Link 1]

### 1）[原题链接][Link 2] ###

### 2）已有题解 ###

### 3）代码 ###

package string;
    
    import java.io.BufferedReader;
    import java.io.IOException;
    import java.io.InputStreamReader;
    
    import static java.lang.System.in;
    
    /**
     * NC100 把字符串转换成整数(atoi)
     */
    public class NC100StringToInt {
        
        public static void main(String[] args) throws IOException {
        
            BufferedReader bf = new BufferedReader(new InputStreamReader(in));
            String str = bf.readLine();
            bf.close();
    
            int res = StrToInt(str);
            System.out.println(res);
        }
    
        /**
         * NC100 把字符串转换成整数(atoi)
         */
        public static int StrToInt(String s) {
        
            //空串
            if (s.isEmpty()) {
        
                return 0;
            }
    
            int length = s.length();
    
            int index = 0;
            //去掉前导空格，如果有
            while (index < length) {
        
                if (s.charAt(index) == ' ') {
        
                    index++;
                } else {
        
                    break;
                }
            }
            //去掉空格就什么都没有了
            if (index == length) {
        
                return 0;
            }
    
            int operator = 1;
            //处理第一个符号是正负号的情况
            if (s.charAt(index) == '+')
                index++;
            else if (s.charAt(index) == '-') {
        
                index++;
                operator = -1;
            }
    
            //去掉符号就什么都没有了
            if (index == length) {
        
                return 0;
            }
    
            int res = 0;
            while (index < length) {
        
                char chr = s.charAt(index);
                //后续非法字符，截断
                if (chr < '0' || chr > '9') {
        
                    break;
                }
                // 处理越界
                // 因为如果越界被显示导致记错错误但是不会报错，所以这里才往前推判断出界
                // 基于公式res = res * 10 + operator * (chr - '0');
                // Integer.MAX_VALUE 2147483647
                // Integer.MAX_VALUE / 10 214748364
                // Integer.MAX_VALUE % 10 7
                // 如上值就会理解为何要如此判断
                if (res > Integer.MAX_VALUE / 10 || (res == Integer.MAX_VALUE / 10 && (chr - '0') > Integer.MAX_VALUE % 10)) {
        
                    return Integer.MAX_VALUE;
                }
                // Integer.MAX_VALUE -2147483648
                // Integer.MAX_VALUE / 10 -214748364
                // Integer.MAX_VALUE % 10 -8
                if (res < Integer.MIN_VALUE / 10 || (res == Integer.MIN_VALUE / 10 && (chr - '0') > -(Integer.MIN_VALUE % 10))) {
        
                    return Integer.MIN_VALUE;
                }
                res = res * 10 + operator * (chr - '0');
                index++;
            }
    
            return res;
        }
    }

[HJ]: https://www.nowcoder.com/exam/oj/ta?tpId=37
[NC]: https://www.nowcoder.com/exam/oj
[offer_ JZ]: https://www.nowcoder.com/exam/oj/ta?page=1&tpId=13&type=13
[Link 1]: https://leetcode.cn/problemset/all/
[Link 2]: https://www.nowcoder.com/practice/d11471c3bf2d40f38b66bb12785df47f?tpId=196&tqId=37088&rp=1&ru=/exam/oj&qru=/exam/oj&sourceUrl=/exam/oj?page=1&pageSize=50&search=NC100&tab=%25E7%25AE%2597%25E6%25B3%2595%25E7%25AF%2587&topicId=196&difficulty=undefined&judgeStatus=undefined&tags=&title=NC100