leetcode 8. String to Integer (atoi) 字符串转数字

末蓝、 2022-06-09 06:48 143阅读 0赞

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.

Update (2015-02-10):  
The signature of the C++ function had been updated. If you still see your function signature accepts a const char \* argument, please click the reload button to reset your code definition.

题意不说了，思想也很简单，但是要注意处理各种可能出现的exception，这道题考察的主要就是对各种exception的判断和处理。

代码如下：

import java.util.ArrayList;
    
    
    public class Solution 
    {
        
         public int myAtoi(String str)
         {
    
             if (str == null || str.length() < 1)
                    return 0;
    
                // trim white spaces
                str = str.trim();
    
                boolean flag = true;
    
                // check negative or positive
                int i = 0;
                if (str.charAt(0) == '-') 
                {
                    flag = false;
                    i++;
                } else if (str.charAt(0) == '+') 
                {
                    flag=true;
                    i++;
                }
                // use double to store result
                double result = 0;
    
                // calculate value
                while (str.length() > i && str.charAt(i) >= '0' && str.charAt(i) <= '9') 
                {
                    result = result * 10 + (str.charAt(i) - '0');
                    i++;
                }
    
                if (flag == false)
                    result = -result;
    
                // handle max and min
                if (result > Integer.MAX_VALUE)
                    return Integer.MAX_VALUE;
    
                if (result < Integer.MIN_VALUE)
                    return Integer.MIN_VALUE;
    
                return (int) result;
         }
    
    
        public static void main(String[] args) 
        {
            Solution solution=new Solution();
            System.out.println(solution.myAtoi("2147483648"));
        }
    }

C++做法如下：

#include <iostream>
    #include <string>
    #include <limits>
    using namespace std;
    
    /*
        下面的做法是做不到AC的，但是可以处理各种情况
        这道题最麻烦的就是各种乱七八糟的输入字符串
    */
    class Solution 
    {
    public:
        int myAtoi(string str)
        {
            return atoi(str.c_str());
        }
    };

下面是AC的代码：

#include <iostream>
    #include <vector>
    #include <map>
    #include <unordered_map>
    #include <set>
    #include <unordered_set>
    #include <queue>
    #include <stack>
    #include <string>
    #include <climits>
    #include <algorithm>
    #include <sstream>
    #include <functional>
    #include <bitset>
    #include <numeric>
    #include <cmath>
    #include <regex>
    #include <iomanip>
    #include <cstdlib>
    #include <ctime>
    
    using namespace std;
    
    
    class Solution 
    {
    public:
        int myAtoi(string str) 
        {
            if (str.empty()) 
                return 0;
    
            int sign = 1, base = 0, i = 0, n = str.size();
            while (i < n && str[i] == ' ') 
                ++i;
    
            if (str[i] == '+' || str[i] == '-')
                sign = (str[i++] == '+') ? 1 : -1;
    
            while (i < n && str[i] >= '0' && str[i] <= '9')
            {
                if (base > INT_MAX / 10 || (base == INT_MAX / 10 && str[i] - '0' > 7))
                    return (sign == 1) ? INT_MAX : INT_MIN;
    
                base = 10 * base + (str[i++] - '0');
            }
            return base * sign;
        }
    };