题解 | 数字阶梯求和

#include<iostream>
#include<vector>
#include<cmath>
using namespace std;

int main() {
	char a;
	int n;
	cin >> a >> n;
	const int N = 1010;
	int arr[N] = {0};
	for (int i = 1; i <= n; i++) {
		string s;
		int temp = i;
		while (temp) {
			s += a;
			temp--;
		}
		for (int j = 0; j < s.length(); j++) {
			arr[s.length() - 1 - j] += s[j] - '0';
		}

	}
	for (int i = 0; i <= n; i++) {
		if (arr[i] >= 10) {
			arr[i + 1] += arr[i] / 10;
			arr[i] %= 10;
		}
	}
	if (arr[n] == 0) {
		for (int i = n-1; i >=0; i--) {
			cout << arr[i];
		}
	}
	else {
		for (int i = n; i >=0; i--) {
			cout << arr[i];
		}
	}
	
}