题解 | #数字阶梯求和#

//土尔逊Torson 编写于2023/05/27
#define _CRT_SECURE_NO_WARNINGS
#include <iostream>
#include <cstdio>
#include <string>
#include <cstring>

using namespace std;

const int MAXN = 10000;

struct BigInteger08401 {
	int digit[MAXN];
	int length;
	BigInteger08401();
	BigInteger08401(int x);
	BigInteger08401 operator=(string str);
	BigInteger08401 operator+(const BigInteger08401& b);
	BigInteger08401 operator*(const BigInteger08401& b);
	friend istream& operator>>(istream& in, BigInteger08401& x);
	friend ostream& operator<<(ostream& out, const BigInteger08401& x);
};

istream& operator>>(istream& in, BigInteger08401& x) {
	string str;
	in >> str;
	x = str;
	return in;
}

ostream& operator<<(ostream& out, const BigInteger08401& x) {
	for (int i = x.length - 1; i >= 0; --i) {
		out << x.digit[i];
	}
	return out;
}

BigInteger08401::BigInteger08401() {
	memset(digit, 0, sizeof(digit));
	length = 0;
}

BigInteger08401::BigInteger08401(int x) {
	memset(digit, 0, sizeof(digit));
	length = 0;
	if (x == 0) {
		digit[length++] = x;
	}
	while (x != 0) {
		digit[length++] = x % 10;
		x /= 10;
	}
}

BigInteger08401 BigInteger08401::operator=(string str) {
	memset(digit, 0, sizeof(digit));
	length = str.size();
	for (int i = 0; i < length; ++i) {
		digit[i] = str[length - i - 1] - '0';
	}
	return *this;
}

BigInteger08401 BigInteger08401::operator+(const BigInteger08401& b) {
	BigInteger08401 answer;
	int carry = 0;
	for (int i = 0; i < length || i < b.length; ++i) {
		int current = carry + digit[i] + b.digit[i];
		carry = current / 10;
		answer.digit[answer.length++] = current % 10;
	}
	if (carry != 0) {
		answer.digit[answer.length++] = carry;
	}
	return answer;
}

BigInteger08401 BigInteger08401::operator*(const BigInteger08401& b) {
	BigInteger08401 answer;
	answer.length = length + b.length;
	for (int i = 0; i < length; ++i) {
		for (int j = 0; j < b.length; ++j) {
			answer.digit[i + j] += digit[i] * b.digit[j];
		}
	}
	for (int i = 0; i < answer.length; ++i) {
		answer.digit[i + 1] += answer.digit[i] / 10;
		answer.digit[i] %= 10;
	}
	while (answer.digit[answer.length - 1] == 0 && answer.length > 1) {
		answer.length--;
	}
	return answer;
}

int main() {
	int a, n;
	while (scanf("%d%d", &a, &n) != EOF) {
		BigInteger08401 Q(a);
		BigInteger08401 answer(0);
		for (int i = 1; i <= n; ++i) {
			for (int j = 1; j < i; ++j) {
				Q.digit[j] = a;
				Q.length++;
			}
			answer = answer + Q;
			Q = a;
		}
		cout << answer << endl;
	}
	system("pause");
	return EXIT_SUCCESS;
}
// 64 位输出请用 printf("%lld")