高精度計算

#define MAXN 9999  
#define MAXSIZE 1010  
#define DLEN 4  
class BigNum {
private:
    int a[5000]; //可以控制大數的位數  
    int len;
public:
    BigNum() {
        len = 1;memset(a,0,sizeof(a));
    } //構造函數  
    BigNum(const long long); //將一個int類型的變量轉化成大數  
    BigNum(const char*); //將一個字符串類型的變量轉化爲大數  
    BigNum(const BigNum &); //拷貝構造函數  
    BigNum &operator=(const BigNum &); //重載賦值運算符，大數之間進行賦值運算  
    friend istream& operator >> (istream&,BigNum&); //重載輸入運算符  
    friend ostream& operator<<(ostream&,BigNum&); //重載輸出運算符  
    BigNum operator+(const BigNum &)const; //重載加法運算符，兩個大數之間的相加運算  
    BigNum operator-(const BigNum &)const; //重載減法運算符，兩個大數之間的相減運算  
    BigNum operator*(const BigNum &)const; //重載乘法運算符，兩個大數之間的相乘運算  
    BigNum operator/(const int &)const; //重載除法運算符，大數對一個整數進行相除運算  
    BigNum operator^(const int &)const; //大數的n次方運算  
    int operator%(const int &)const; //大數對一個int類型的變量進行取模運算  
    bool operator>(const BigNum &T)const; //大數和另一個大數的大小比較  
    bool operator>(const int &t)const; //大數和一個int類型的變量的大小比較  
    void print(); //輸出大數  
    void read(const char *s); //從字符串讀入  
    void pre0(char *s); //取出字符串的前導0;  
};
BigNum::BigNum(const long long b) //將一個int類型的變量轉化爲大數  
{
    long long c,d = b;
    len = 0;
    memset(a,0,sizeof(a));
    while(d>MAXN) {
        c = d - (d / (MAXN + 1))*(MAXN + 1);
        d = d / (MAXN + 1);
        a[len++] = c;
    }
    a[len++] = d;
}
BigNum::BigNum(const char *s) //將一個字符串類型的變量轉化爲大數  
{
    int t,k,index,L,i;
    memset(a,0,sizeof(a));
    L = strlen(s);
    len = L / DLEN;
    if(L%DLEN)len++;
    index = 0;
    for(i = L - 1;i >= 0;i -= DLEN) {
        t = 0;
        k = i - DLEN + 1;
        if(k<0)k = 0;
        for(int j = k;j <= i;j++)
            t = t * 10 + s[j] - '0';
        a[index++] = t;
    }
}
BigNum::BigNum(const BigNum &T):len(T.len) //拷貝構造函數  
{
    int i;
    memset(a,0,sizeof(a));
    for(i = 0;i<len;i++)
        a[i] = T.a[i];
}
BigNum & BigNum::operator=(const BigNum &n) //重載賦值運算符，大數之間賦值運算  
{
    int i;
    len = n.len;
    memset(a,0,sizeof(a));
    for(i = 0;i<len;i++)
        a[i] = n.a[i];
    return *this;
}
istream& operator >> (istream &in,BigNum &b) {
    char ch[MAXSIZE * 4];
    int i = -1;
    in >> ch;
    int L = strlen(ch);
    int count = 0,sum = 0;
    for(i = L - 1;i >= 0;) {
        sum = 0;
        int t = 1;
        for(int j = 0;j<4 && i >= 0;j++,i--,t *= 10) {
            sum += (ch[i] - '0')*t;
        }
        b.a[count] = sum;
        count++;
    }
    b.len = count++;
    return in;
}
ostream& operator<<(ostream& out,BigNum& b) //重載輸出運算符  
{
    int i;
    cout << b.a[b.len - 1];
    for(i = b.len - 2;i >= 0;i--) {
        printf("%04d",b.a[i]);
    }
    return out;
}
BigNum BigNum::operator+(const BigNum &T)const //兩個大數之間的相加運算  
{
    BigNum t(*this);
    int i,big;
    big = T.len>len ? T.len : len;
    for(i = 0;i<big;i++) {
        t.a[i] += T.a[i];
        if(t.a[i]>MAXN) {
            t.a[i + 1]++;
            t.a[i] -= MAXN + 1;
        }
    }
    if(t.a[big] != 0)
        t.len = big + 1;
    else t.len = big;
    return t;
}
BigNum BigNum::operator-(const BigNum &T)const //兩個大數之間的相減運算  
{
    int i,j,big;
    bool flag;
    BigNum t1,t2;
    if(*this>T) {
        t1 = *this;
        t2 = T;
        flag = 0;
    } else {
        t1 = T;
        t2 = *this;
        flag = 1;
    }
    big = t1.len;
    for(i = 0;i<big;i++) {
        if(t1.a[i]<t2.a[i]) {
            j = i + 1;
            while(t1.a[j] == 0)
                j++;
            t1.a[j--]--;
            while(j>i)
                t1.a[j--] += MAXN;
            t1.a[i] += MAXN + 1 - t2.a[i];
        } else t1.a[i] -= t2.a[i];
    }
    t1.len = big;
    while(t1.a[len - 1] == 0 && t1.len>1) {
        t1.len--;
        big--;
    }
    if(flag)
        t1.a[big - 1] = 0 - t1.a[big - 1];
    return t1;
}
BigNum BigNum::operator*(const BigNum &T)const //兩個大數之間的相乘  
{
    BigNum ret;
    int i,j,up;
    int temp,temp1;
    for(i = 0;i<len;i++) {
        up = 0;
        for(j = 0;j<T.len;j++) {
            temp = a[i] * T.a[j] + ret.a[i + j] + up;
            if(temp>MAXN) {
                temp1 = temp - temp / (MAXN + 1)*(MAXN + 1);
                up = temp / (MAXN + 1);
                ret.a[i + j] = temp1;
            } else {
                up = 0;
                ret.a[i + j] = temp;
            }
        }
        if(up != 0)
            ret.a[i + j] = up;
    }
    ret.len = i + j;
    while(ret.a[ret.len - 1] == 0 && ret.len>1)ret.len--;
    return ret;
}
BigNum BigNum::operator/(const int &b)const //大數對一個整數進行相除運算  
{
    BigNum ret;
    int i,down = 0;
    for(i = len - 1;i >= 0;i--) {
        ret.a[i] = (a[i] + down*(MAXN + 1)) / b;
        down = a[i] + down*(MAXN + 1) - ret.a[i] * b;
    }
    ret.len = len;
    while(ret.a[ret.len - 1] == 0 && ret.len>1)
        ret.len--;
    return ret;
}
int BigNum::operator%(const int &b)const //大數對一個 int類型的變量進行取模  
{
    int i,d = 0;
    for(i = len - 1;i >= 0;i--)
        d = ((d*(MAXN + 1)) % b + a[i]) % b;
    return d;
}
BigNum BigNum::operator^(const int &n)const //大數的n次方運算  
{
    BigNum t,ret(1);
    int i;
    if(n<0)exit(-1);
    if(n == 0)return 1;
    if(n == 1)return *this;
    int m = n;
    while(m>1) {
        t = *this;
        for(i = 1;(i << 1) <= m;i <<= 1)
            t = t*t;
        m -= i;
        ret = ret*t;
        if(m == 1)ret = ret*(*this);
    }
    return ret;
}
bool BigNum::operator>(const BigNum &T)const //大數和另一個大數的大小比較  
{
    int ln;
    if(len>T.len)return true;
    else if(len == T.len) {
        ln = len - 1;
        while(a[ln] == T.a[ln] && ln >= 0)
            ln--;
        if(ln >= 0 && a[ln]>T.a[ln])
            return true;
        else
            return false;
    } else
        return false;
}
bool BigNum::operator>(const int &t)const //大數和一個int類型的變量的大小比較  
{
    BigNum b(t);
    return *this>b;
}
void BigNum::print() //輸出大數  
{
    int i;
    printf("%d",a[len - 1]);
    for(i = len - 2;i >= 0;i--)
        printf("%04d",a[i]);
    printf("\n");
}
void BigNum::read(const char *s) {
    int t,k,index,L,i;
    memset(a,0,sizeof(a));
    L = strlen(s);
    len = L / DLEN;
    if(L%DLEN)len++;
    index = 0;
    for(i = L - 1; i >= 0; i -= DLEN) {
        t = 0;
        k = i - DLEN + 1;
        if(k < 0)k = 0;
        for(int j = k; j <= i; j++)
            t = t * 10 + s[j] - '0';
        a[index++] = t;
    }
}
void BigNum::pre0(char *s) {
    int pos = 0;
    int len = strlen(s);
    for(int i = 0;i < len;i++) {
        if(s[i] != '0') {
            pos = i;
            break;
        }
    }
    for(int i = pos;i < len;i++)
        s[i - pos] = s[i];
    s[len - pos] = '\0';
}
讀入輸出