算法___大整数运算

#include <iostream>
#include <stdio.h>
#include <string.h>
#include <string>
#include <stdlib.h>
#include <algorithm>
using namespace std;
string MULTIPLY_INT(string str1 , string str2);
string MINUS_INT(string str1 , string str2);
inline int compare(string str1 , string str2)
{
    if(str1.size() > str2.size())//初步比较 长度长的整数大
        return 1;
    else if(str1.size() < str2.size())
        return -1;
    else
        return str1.compare(str2);
    //若两数长度相等，按位比较，compare函数 ：相等返回0， 大于返回1，否则返回-1
}

//高精度加法
string ADD_INT(string str1 , string str2)
{
    int sign = 1;//符号位
    string str;
    if(str1[0] == '-')
    {
        if(str2[0] == '-')
        {
            sign = -1;
            str = ADD_INT(str1.erase(0,1) , str2.erase(0,1));
        }
        else
            str = MINUS_INT(str2 , str1.erase(0,1));
    }
    else
    {
        if(str2[0] == '-')
            str = MINUS_INT(str1 , str2.erase(0,1));
        else//把两个数，短整数前加0补齐
        {
            string :: size_type len1,len2;
            int i;
            len1 = str1.size();
            len2 = str2.size();
            if(len1 < len2)
            {
                for( i =1 ; i <= len2 - len1 ; i++)
                    str1 = "0" + str1;
            }
            else if(len1 > len2)
            {
                for(i = 1 ; i <= len1 - len2 ; i++)
                    str2 = "0" + str2;
            }
            int int1 = 0 , int2 = 0 ;//int2 记录进位
            for( i = str1.size() - 1 ; i >= 0 ; i--)
            {
                int1 = (int (str1[i]) - 48 + int(str2[i]) - 48 + int2) % 10;//48 ASCII of 0
                int2 = (int (str1[i]) - 48 + int(str2[i]) - 48 + int2) / 10;
                str = char(int1 + 48) + str;
            }
            if(int2 != 0)
                str = char(int2 + 48) + str;
        }
    }
    //处理符号位
    if((sign == -1) && (str[0] != '0'))
        str = "-" + str;
    return str;
}

//高精度减法
string MINUS_INT (string str1 , string str2)
{
    int sign = 1;// 符号位
    string str;
    if(str2[0] == '-')
        str = ADD_INT(str1 , str2);
    else
    {
        int res = compare(str1 , str2);
        if(res == 0)
            return "0";
        if(res < 0)
        {
            sign = -1;
            string temp = str1;
            str1 = str2;
            str2 = temp;
        }
        string :: size_type tempint;
        tempint = str1.size() - str2.size();//两数相差位数
        for(int i = str2.size() -1 ; i >= 0 ; i--)//str2.size() -1 str2 最低位
        {
            if(str1[i + tempint] < str2[i])//str1[i + tempint] 与str2 对应位数的数
            {
                str1[i + tempint -1] = char(int (str1[i + tempint - 1])-1);//借位 高位减一
                str = char(str1[i + tempint] - str2[i] + 58) + str;// 58 ASCII of 10
            }
            else
                str = char(str1[i + tempint] - str2[i] + 48) + str;

        }
        for(int i = tempint -1 ; i >=0 ; i--)
            str = str1[i] + str;//将数补全
    }
    //去除结果中多余的前导0
    str.erase(0,str.find_first_not_of('0'));
    if(str.empty())
        str = "0";
    if((sign == -1) && str[0] != '0')
        str = "-" + str;
    return str;
}

//高精度乘法
string MULTIPLY_INT(string str1 , string str2)
{
    int sign = 1;//符号位
    string str;
    if(str1[0] == '-')
    {
        sign *= -1;
        str1 = str1.erase(0,1);
    }
    if(str2[0] == '-')
    {
        sign *= -1;
        str2 = str2.erase(0,1);
    }
    int i,j;
    string :: size_type len1,len2;
    len1 = str1.size();
    len2 = str2.size();
    for(i = len2 - 1 ; i >= 0 ; i--)//实现手工乘法
    {
        string tempstr;
        int int1 = 0 , int2 = 0 , int3 = int(str2[i]) - 48;
        if(int3 != 0)
        {
            for(j = 1 ; j <= (int)(len2 - 1 - i) ; j++)
                tempstr = "0" + tempstr;
            for(j = len1 - 1 ; j >= 0 ; j--)
            {
                int1 = (int3 * (int(str1[j]) - 48) + int2) % 10;
                int2 = (int3 * (int(str1[j]) - 48) + int2) / 10;
                tempstr = char(int1 + 48) + tempstr;
            }
            if(int2 != 0)
                tempstr = char(int2 + 48) + tempstr;
        }
                str = ADD_INT(str,tempstr);
    }
        //去除结果中的前导0
    str.erase(0,str.find_first_not_of('0'));
    if(str.empty())
        str = "0";
    if((sign == -1) && (str[0] != '0'))
        str += "-" + str;
    return str;
}
string DIVIDE_INT(string str1, string str2, int flag)
{
    //flag = 1时,返回商; flag = 0时,返回余数
    string quotient, residue;
    int sign1 = 1, sign2 = 1, i;
    if(str2 == "0")
    {                                 //判断除数是否为0
        quotient = "ERROR!";
        residue = "ERROR!";
        if(flag == 1) return quotient;
        else return residue;
    }
    if(str1 == "0")
    {                                 //判断被除数是否为0
        quotient = "0";
        residue = "0";
    }
    if(str1[0] == '-')
    {
        str1 = str1.erase(0, 1);
        sign1 *= -1;
        sign2 = -1;
    }
    if(str2[0] == '-')
    {
        str2 = str2.erase(0, 1);
        sign1 *= -1;
    }
    int res = compare(str1, str2);
    if(res < 0)
    {
        quotient = "0";
        residue = str1;
    }
    else if(res == 0)
    {
        quotient = "1";
        residue = "0";
    }
    else
    {
        string::size_type len1, len2;
        len1 = str1.size(); len2 = str2.size();
        string tempstr;
        tempstr.append(str1, 0, len2 - 1);

        //模拟手工除法
        for(i = len2 - 1; i < len1; i++)
        {
            tempstr = tempstr + str1[i];
            for(char ch = '9'; ch >= '0'; ch --)
            {
                string str;
                str = str + ch;
                if(compare(MULTIPLY_INT(str2, str), tempstr) <= 0)
                {
                    quotient = quotient + ch;
                    tempstr = MINUS_INT(tempstr, MULTIPLY_INT(str2, str));
                    break;
                }
            }
        }
        residue = tempstr;
    }

    //去除结果中的前导0
    quotient.erase(0, quotient.find_first_not_of('0'));
    if(quotient.empty()) quotient = "0";
    if((sign1 == -1) && (quotient[0] !='0'))
        quotient = "-" + quotient;
    if((sign2 == -1) && (residue[0] !='0'))
        residue = "-" + residue;
    if(flag == 1) return quotient;
    else return residue;
}

//高精度除法,返回商
string DIV_INT(string str1, string str2)
{
    return DIVIDE_INT(str1, str2, 1);
}

//高精度除法,返回余数
string MOD_INT(string str1, string str2)
{
    return DIVIDE_INT(str1, str2, 0);
}

 基本照模板敲的，感觉要gg了