zoukankan      html  css  js  c++  java
  • LeetCode-String to Integer (atoi)

    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.

    Notes: It is intended for this problem to be specified vaguely (ie, no given input specs). You are responsible to gather all the input requirements up front.

    Requirements for atoi:

    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. If the correct value is out of the range of representable values, INT_MAX (2147483647) or INT_MIN (-2147483648) is returned.

    class Solution {
    public:
        int atoi(const char *str) {
            // Start typing your C/C++ solution below
            // DO NOT write int main() function
            int i=0;
            int ret=0;
            int length=0;
            bool start=false;//jump head spaces
            bool neg=false;// if negative
            bool end=false;//jump tail spaces
            while(str[i]!='')
            {
                if(start){
                    if(str[i]>='0'&&str[i]<='9'){
                        
                        if(ret>214748364){
                            if(neg){
                                ret= -2147483648;
                                end=true;
                            }
                            else {
                                ret= 2147483647;
                                end=true;
                            }
                        }
                        if(!end)
                        ret*=10;
                        if(neg){
                             if(str[i]-'0'-1>2147483647-ret)
                             {
                                ret= -2147483648;
                                end=true;
                             }
                        }
                        else{
                            if(str[i]-'0'>2147483647-ret)
                            {
                                ret=2147483647;
                                end =true;
                            }
                            
                        }
                       if(!end)
                        ret+=str[i]-'0';
                    }
                    else{
    
                            if(neg)ret=-ret;
                            return ret;
                    }
                }
                else
                {
                    
                    if(str[i]>='0'&&str[i]<='9'){
                        start=true;
                        ret+=str[i]-'0';
                        length++;
                    }else if
                    (str[i]=='+'){start=true;
                    
                    }
                    else if(str[i]=='-'){
                    start=true;
                    neg=true;
                    }
                    else if(str[i]!=' '){return 0;}
                }
                i++;
            }
            if(neg)ret=-ret;
            return ret;
        }
    };
  • 相关阅读:
    前端知识体系
    前端知识大总结(全)
    控制div层的显示以及隐藏
    让一个比较宽的banner位于页面中间
    数据结构之树(二)
    数据结构之树(一)
    数据结构之队列
    数据结构之栈
    数据结构之线性表(二)
    数据结构之线性表(一)
  • 原文地址:https://www.cnblogs.com/superzrx/p/3295792.html
Copyright © 2011-2022 走看看