Initial commit

2019/republic/12_d2/pante.cpp

@@ -0,0 +1,143 @@
+#include <iostream>
+#include <fstream>
+
+using namespace std;
+
+ifstream input_stream;
+ofstream output_stream;
+
+bool checkAscending(string numStr) {
+	char highestDigit = numStr[0];
+
+	for (uint8_t i = 1; i < numStr.length(); i++) {
+		if (numStr[i] < highestDigit) {
+			return false;
+		}
+		highestDigit = numStr[i];
+	}
+	return true;
+}
+
+
+
+uint64_t n_choose_m(uint8_t n, uint8_t m) {
+	if (m > n) {
+		return 0;
+	}
+
+	if (m * 2 > n) {
+		m = n - m;
+	}
+
+	if (m == 0) {
+		return 1;
+	}
+
+	uint64_t res = n;
+
+	for (int i = 2; i <= m; i++) {
+		res *= n - i + 1;
+		res /= i;
+	}
+
+	return res;
+}
+
+
+
+uint64_t pos_combinations(uint8_t pos) {
+	/**
+	pos starts at 0 from right end of number
+	10^pos <> 10^pos-1
+	*/
+	if (pos == 0) {
+		return 0;
+	} else {
+		return n_choose_m(8 + pos, pos);
+	}
+}
+
+
+
+uint64_t following_combinations(uint8_t first_num, uint8_t pos) {
+	/**
+	10^pos+1 <> first_num * 10^pos
+	available = 10 - (first_num - 1) + allowed_repeats (pos)
+	*/
+	return n_choose_m(10 - first_num + pos, pos + 1);
+}
+
+
+
+uint64_t preceeding_combinations(uint8_t first_num, uint8_t pos) {
+	/**
+	first_num * 10^pos <> 10^pos
+	*/
+	return pos_combinations(pos + 1) - following_combinations(first_num, pos);
+}
+
+
+
+uint64_t find_ascending(string start, string end) {
+	uint64_t result = 0;
+	const uint8_t end_len = end.length();
+
+	if (end_len == 1) {
+		result += stoi(end) - stoi(start) + 1;
+	} else if (start == "1") {
+		char highest_digit = '1';
+		bool sequence_integrity = true;
+
+		// Run this loop until a digit lower than the others is encountered
+		uint8_t i;
+		for (i = 0; i < end_len - 1; i++) {
+			uint8_t pos = end_len - i - 1;
+			result += pos_combinations(pos);
+
+			if (end[i] > highest_digit) {
+				result += preceeding_combinations(end[i] - '0', pos) - preceeding_combinations(highest_digit - '0', pos);
+				highest_digit = end[i];
+			} else if (end[i] < highest_digit) {
+				sequence_integrity = false;
+				break;
+			}
+		}
+
+		i++;
+		for (i; i < end_len - 1; i++) {
+			uint8_t pos = end_len - i - 1;
+			result += pos_combinations(pos);
+		}
+
+		if (sequence_integrity && end[end_len - 1] >= highest_digit) {
+			result += end[end_len - 1] - highest_digit + 1;
+		}
+	} else {
+		result += find_ascending("1", end) - find_ascending("1", start);
+
+		if (checkAscending(start)) {
+			result += 1;
+		}
+	}
+
+	return result;
+}
+
+
+
+int main() {
+	input_stream.open("input.txt");
+	output_stream.open("output.txt");
+
+	string A; 
+	string B;
+
+	input_stream >> A;
+	input_stream >> B;
+	
+	cout << find_ascending(A, B) << endl;
+
+	input_stream.close();
+	output_stream.close();
+	return 0;
+}