OI-codes/templates/BigInt.h

#include <algorithm>
#include <iostream>
#include <string>

class BigInt {
  public:
    int sign;
    std::string s;

    BigInt() {
        s = "";
    }

    BigInt(std::string x) {
        *this = x;
    }

    BigInt(int x) {
        *this = std::to_string(x);
    }

    BigInt negative() {
        BigInt x = *this;
        x.sign *= -1;
        return x;
    }

    BigInt normalize(int newSign) {
        for (int a = s.size() - 1; a > 0 && s[a] == '0'; a--) {
            s.erase(s.begin() + a);
        }
        sign = (s.size() == 1 && s[0] == '0' ? 1 : newSign);
        return *this;
    }

    void operator=(std::string x) {
        int newSign = (x[0] == '-' ? -1 : 1);
        s = (newSign == -1 ? x.substr(1) : x);
        std::reverse(s.begin(), s.end());
        this->normalize(newSign);
    }

    bool operator==(const BigInt& x) const {
        return (s == x.s && sign == x.sign);
    }

    bool operator<(const BigInt& x) const {
        if (sign != x.sign) {
            return sign < x.sign;
        }
        if (s.size() != x.s.size()) {
            return (sign == 1 ? s.size() < x.s.size() : s.size() > x.s.size());
        }
        for (int a = s.size() - 1; a >= 0; a--) {
            if (s[a] != x.s[a]) {
                return (sign == 1 ? s[a] < x.s[a] : s[a] > x.s[a]);
            }
        }

        return false;
    }

    bool operator<=(const BigInt& x) const {
        return (*this < x || *this == x);
    }

    bool operator>(const BigInt& x) const {
        return (!(*this < x) && !(*this == x));
    }

    bool operator>=(const BigInt& x) const {
        return (*this > x || *this == x);
    }

    BigInt operator+(BigInt x) {
        BigInt curr = *this;
        if (curr.sign != x.sign) return curr - x.negative();
        BigInt res;
        for (int a = 0, carry = 0; a < s.size() || a < x.s.size() || carry; a++) {
            carry += (a < curr.s.size() ? curr.s[a] - '0' : 0) + (a < x.s.size() ? x.s[a] - '0' : 0);
            res.s += (carry % 10 + '0');
            carry /= 10;
        }
        return res.normalize(sign);
    }

    BigInt operator-(BigInt x) {
        BigInt curr = *this;
        if (curr.sign != x.sign) return curr + x.negative();
        int realSign = curr.sign;
        curr.sign = x.sign = 1;
        if (curr < x) return ((x - curr).negative()).normalize(-realSign);
        BigInt res;
        for (int a = 0, borrow = 0; a < s.size(); a++) {
            borrow = (curr.s[a] - borrow - (a < x.s.size() ? x.s[a] : '0'));
            res.s += (borrow >= 0 ? borrow + '0' : borrow + '0' + 10);
            borrow = (borrow >= 0 ? 0 : 1);
        }
        return res.normalize(realSign);
    }

    BigInt operator*(BigInt x) {
        BigInt res("0");
        for (int a = 0, b = s[a] - '0'; a < s.size(); a++, b = s[a] - '0') {
            while (b--) res = (res + x);
            x.s.insert(x.s.begin(), '0');
        }
        return res.normalize(sign * x.sign);
    }

    BigInt operator/(BigInt x) {
        if (x.s.size() == 1 && x.s[0] == '0') {
            x.s[0] /= (x.s[0] - '0');
        }
        BigInt temp("0"), res;
        for (int a = 0; a < s.size(); a++) res.s += "0";
        int newSign = sign * x.sign;
        x.sign = 1;
        for (int a = s.size() - 1; a >= 0; a--) {
            temp.s.insert(temp.s.begin(), '0');
            temp = temp + s.substr(a, 1);
            while (!(temp < x)) {
                temp = temp - x;
                res.s[a]++;
            }
        }
        return res.normalize(newSign);
    }

    BigInt operator%(BigInt x) {
        if (x.s.size() == 1 && x.s[0] == '0') {
            x.s[0] /= (x.s[0] - '0');
        }
        BigInt res("0");
        x.sign = 1;
        for (int a = s.size() - 1; a >= 0; a--) {
            res.s.insert(res.s.begin(), '0');
            res = res + s.substr(a, 1);
            while (!(res < x)) res = res - x;
        }
        return res.normalize(sign);
    }

    std::string toString() const {
        std::string ret = s;
        std::reverse(ret.begin(), ret.end());
        return (sign == -1 ? "-" : "") + ret;
    }

    BigInt toBase10(int base) {
        BigInt exp(1), res("0"), BASE(base);
        for (int a = 0; a < s.size(); a++) {
            int curr = (s[a] < '0' || s[a] > '9' ? (toupper(s[a]) - 'A' + 10) : (s[a] - '0'));
            res = res + (exp * BigInt(curr));
            exp = exp * BASE;
        }
        return res.normalize(sign);
    }

    BigInt toBase10(int base, BigInt mod) {
        BigInt exp(1), res("0"), BASE(base);
        for (int a = 0; a < s.size(); a++) {
            int curr = (s[a] < '0' || s[a] > '9' ? (toupper(s[a]) - 'A' + 10) : (s[a] - '0'));
            res = (res + ((exp * BigInt(curr) % mod)) % mod);
            exp = ((exp * BASE) % mod);
        }
        return res.normalize(sign);
    }

    std::string convertToBase(int base) {
        BigInt ZERO(0), BASE(base), x = *this;
        std::string modes = "0123456789ABCDEFGHIJKLMNOPQRSTUVWXYZ";
        if (x == ZERO) {
            return "0";
        }
        std::string res = "";
        while (x > ZERO) {
            BigInt mod = x % BASE;
            x = x - mod;
            if (x > ZERO) x = x / BASE;
            res = modes[stoi(mod.toString())] + res;
        }
        return res;
    }

    BigInt toBase(int base) {
        return BigInt(this->convertToBase(base));
    }

    friend std::istream& operator>>(std::istream& is, BigInt& x) {
        std::string s;
        is >> s;
        x = BigInt(s);
        return is;
    }

    friend std::ostream& operator<<(std::ostream& os, const BigInt& x) {
        os << x.toString();
        return os;
    }
};