题解 | #把字符串转换成整数(atoi)#

#include <climits>
class Solution {
public:
    /**
     * 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
     */
    long long shuzi(long long num, char ch){
        int last = ch - '0';
        num = num * 10 + last;
        return num;
    }

    int StrToInt(string s) {
        // write code here
    int num_index = 0;
    int symbol_index = 1;
    int symbol_num = 0;
    long long num = 0;
    for (auto ch : s){

        if (ch == '-' || ch == '+'){
            if(num_index == 0 && symbol_num == 0){
                if (ch == '-')
                    symbol_index = -1;
                symbol_num++;
            }
            else
                return num * symbol_index;;
        }
        
        if (num_index == 1 && (ch < '0' || ch > '9' ) || isalpha(ch))
            return num * symbol_index;
        
        if (ch >= '0' && ch <= '9'){
            num_index = 1;
            num = shuzi(num, ch);
            if (num > INT_MAX ){
                if (symbol_index == 1)
                    return INT_MAX;
                else
                    return INT_MIN;
            }
        } 
    }
        int result = int(num);
        return result * symbol_index;
    }
};