zoukankan      html  css  js  c++  java
  • [LC] 8. String to Integer (atoi)

    Implement atoi which converts a string to an integer.

    The function first discards as many whitespace characters as necessary until the first non-whitespace character is found. Then, starting from this character, takes an optional initial plus or minus sign followed by as many numerical digits as possible, and interprets them as a numerical value.

    The string can contain additional characters after those that form the integral number, which are ignored and have no effect on the behavior of this function.

    If the first sequence of non-whitespace characters in str is not a valid integral number, or if no such sequence exists because either str is empty or it contains only whitespace characters, no conversion is performed.

    If no valid conversion could be performed, a zero value is returned.

    Note:

    • Only the space character ' ' is considered as whitespace character.
    • Assume we are dealing with an environment which could only store integers within the 32-bit signed integer range: [−231,  231 − 1]. If the numerical value is out of the range of representable values, INT_MAX (231 − 1) or INT_MIN (−231) is returned.

    Example 1:

    Input: "42"
    Output: 42
    

    Example 2:

    Input: "   -42"
    Output: -42
    Explanation: The first non-whitespace character is '-', which is the minus sign.
                 Then take as many numerical digits as possible, which gets 42.
    

    Example 3:

    Input: "4193 with words"
    Output: 4193
    Explanation: Conversion stops at digit '3' as the next character is not a numerical digit.
    

    Example 4:

    Input: "words and 987"
    Output: 0
    Explanation: The first non-whitespace character is 'w', which is not a numerical 
                 digit or a +/- sign. Therefore no valid conversion could be performed.

    Example 5:

    Input: "-91283472332"
    Output: -2147483648
    Explanation: The number "-91283472332" is out of the range of a 32-bit signed integer.
                 Thefore INT_MIN (−231) is returned.

    class Solution {
        public int myAtoi(String str) {
            if (str == null) {
                return 0;
            }
            str = str.trim();
            if (str.length() == 0) {
                return 0;
            }
            int first = 0, sign = 1;
            // assin with long type;
            long res = 0;
            if (str.charAt(0) == '+') {
                first += 1;
            } else if (str.charAt(0) == '-') {
                sign = -1;
                first += 1;
            }
            for (int i = first; i < str.length(); i++) {
                if (!Character.isDigit(str.charAt(i))) {
                    return sign * (int)res;
                }
                res = 10 * res + str.charAt(i) - '0';
                if (sign == 1 && res > Integer.MAX_VALUE) {
                    return Integer.MAX_VALUE;
                }
                if (sign == -1 && res > Integer.MAX_VALUE) {
                    return Integer.MIN_VALUE;
                }        
            }
            return sign * (int)res;
        }
    }
  • 相关阅读:
    对List进行子查询及分组
    网格数据库架构设计构想
    推荐一款简单实用的漏洞测试工具:Paros
    用友U9产品SOA设计架构遭技术质疑
    超简单使用MemCached
    不按常规出招
    如何学好AJax、求高手指点
    Begin
    SpringBoot基础
    SpringBoot基础学习(番外9.1)Spring MVC或Spring Boot配置默认访问页面不生效?
  • 原文地址:https://www.cnblogs.com/xuanlu/p/11875959.html
Copyright © 2011-2022 走看看