(c++) SWEA "1928) Base64 Decoder"

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SW Expert Academy

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#include <iostream>
#include <cctype>
#include <string>
#include <bitset>
#include <cmath>

using namespace std;
int decode(char c) {
	if (isupper(c)) {
		return (c - 'A');
	}
	else if (islower(c)) {
		return (c - 'a' + 26);
	}
	else if (isdigit(c)) {
		return c - '0' + 52;
	}
	else {
		if (c == '+') {
			return 62;
		}
		else {
			return 63;
		}
	}
}

string solution(string str) {
	string answer;
	string nums;
	for (int i = 0; i < str.size();i++) {
		if (i > 0 && i % 4 == 0) {
			for (int j = 0; j < 3; j++) {
				string tmp = nums.substr(j * 8, 8);
				char c = 0;
				for (int k = 0; k < tmp.size(); k++) {
					c += pow(2, 8 - k - 1) * (tmp[k] - '0');
				}
				answer.push_back(c);
			}
			nums = "";
		}
		int num = decode(str[i]);
		nums += bitset<6>(num).to_string();
	}
	//tmp가 남아있을 경우 확인
	for (int j = 0; j < nums.size()/8; j++) {
		string tmp = nums.substr(j * 8, 8);
		char c = 0;
		for (int k = 0; k < tmp.size(); k++) {
			c += pow(2, 8 - k - 1) * (tmp[k] - '0');
		}
		answer.push_back(c);
	}
	return answer;
}

int main() {
	int T; cin >> T;
	for (int t = 1; t <= T; t++) {
		string str; cin >> str;
		cout << "#" << t << " " << solution(str) << endl;
	}
	return 0;
}