hdu1402-大數相乘

1402

。。又逾時了 QAQ

#include<iostream>    
#include<string>    
using namespace std;    
string pre(string &a)  
{  
	int i = 0;  
	if (a[0]!='0') return a;  
	while (a[i] == '0') i++;  
	a = a.substr(i,a.length()-1);   //删除前面的0，如000000007  
	return a ;  
}  
int main()    
{  
	string a,b;//,t;
	int mult,bit,i,j,n;
	bool first;
	while (cin>>a>>b)
	{
		first = true;
		pre(a);
		pre(b);
		string t(a.length()+b.length(),'0');               
		reverse(a.begin(),a.end());
		reverse(b.begin(),b.end());
		for ( i = 0; i <= a.length()-1; i++)
		{	
			bit = 0;
			for ( j = 0; j <= b.length()-1; j++)
			{
				mult = (a[i]-48) * (b[j]-48) + bit;
				bit = mult/10;
				if(first)t[i+j] = mult%10 + 48;     //第一次時候字元0000加上數字
				else {
					n = ((t[i+j] -48)+ mult%10);   //如果剛好加起來是10
					t[i+j] = n%10+ 48;
					if(n>=10) bit ++;
				}
			}
			if(bit!=0)
				t[i+j++] = bit+48;
			first = false;
		}
		reverse(t.begin(),t.end());
		if(t[0] == '0') t = t.substr(1,t.length() - 1);  
		cout<<t<<endl;
	}

	return 0;    
}