solution

• 每位权值不同的高精度加法
• 测试点5：结果为0的情况

#include<iostream>
#include<string>
using namespace std;
int main(){
	string rule, a, b, ans = "";
	int carry = 0, temp, cnt, power;
	cin >> rule >> a >> b;
	for(int i = a.size() - 1, j = b.size() - 1, cnt = rule.size() - 1; i >= 0 || j >= 0; i--, j--, cnt--){
		if(i < 0) temp = b[j] - '0' + carry;
		else if(j < 0) temp = a[i] - '0' + carry;
		else temp = (a[i] - '0') + (b[j] - '0') + carry;
		if(rule[cnt] == '0') power = 10;
		else power = rule[cnt] - '0';
		ans = to_string(temp % power) + ans;
		carry = temp / power;
	}
	if(carry) ans = to_string(carry) + ans;
	while(ans[0] == '0') ans.erase(0, 1); 
	if(ans.size() == 0) cout << 0;
	else cout << ans;
	return 0;
} 

or

#include<iostream>
#include<string>
using namespace std;
int main(){
	string rule, a, b, ans = "";
	int carry = 0, temp, cnt, power;
	cin >> rule >> a >> b;
	while(a.size() < b.size()) a = "0" + a;
	while(b.size() < a.size()) b = "0" + b;
	for(int i = a.size() - 1; i >= 0; i--){
		temp = (a[i] - '0') + (b[i] - '0') + carry;
		if(rule[i] == '0') power = 10;
		else power = rule[i] - '0';
		ans = to_string(temp % power) + ans;
		carry = temp / power;
	}
	if(carry) ans = to_string(carry) + ans;
	while(ans[0] == '0') ans.erase(0, 1); 
	if(ans.size() == 0) cout << 0;
	else cout << ans;
	return 0;
}