题解 | #10进制 VS 2进制#

#include <iostream>
#include<vector>
using namespace std;
//大整数
string Divide(string s,int a)
{
    int remainder=0;
    for(int i=0;i<s.size();i++)
    {
        int current=remainder*10+s[i]-'0';
        s[i]=current/a+'0';
        remainder=current%a;
    }
    int i=0;
    while(s[i]=='0')i++;
    return s.substr(i);
}
string Multiply(string s,int a)
{
    int carry=0;
    for(int i=s.size()-1;i>=0;i--)
    {
        int current=(s[i]-'0')*a+carry;
        s[i]=current%10+'0';
        carry=current/10;
    }
    if(carry!=0)s="1"+s;
    return s;
}
string Add(string s,int a)
{
    int carry=a;
    for(int i=s.size()-1;i>=0;i--)
    {
        int current=s[i]-'0'+carry;
        s[i]=current%10+'0';
        carry=current/10;
    }
    if(carry)s="1"+s;
    return s;
}

int main() {
    string s;
    while (cin >> s) { // 注意 while 处理多个 case
        vector<int>array;
        while(s.size()!=0)
        {
            int last=s[s.size()-1]-'0';
            array.push_back(last%2);
            s=Divide(s,2);
            //cout<<s<<endl;
        }
        //保存的时候已经逆序了
        string ans="0";
        for(int i=0;i<array.size();i++)
        {
            ans=Multiply(ans,2);
            ans=Add(ans,array[i]);
        }
        cout<<ans<<endl;
    }
}
// 64 位输出请用 printf("%lld")