From 723922fbf3a1c5233efe74cb4c0793e2ba4105e1 Mon Sep 17 00:00:00 2001
From: bramtechs <bramtech@telenet.be>
Date: Fri, 13 Dec 2024 23:01:02 +0100
Subject: [PATCH] Day 03 - Part 01 - Fix Parser and add Lexer

---
 src/day03.cc | 81 ++++++++++++++++++++++++++++++++++++++++++----------
 1 file changed, 66 insertions(+), 15 deletions(-)

diff --git a/src/day03.cc b/src/day03.cc
index db2a62c..6c552c2 100644
--- a/src/day03.cc
+++ b/src/day03.cc
@@ -1,7 +1,9 @@
 #include <iostream>
+#include <span>
 #include <stdexcept>
 #include <string>
 #include <string_view>
+#include <utility>
 #include <vector>
 
 static std::string input =
@@ -27,22 +29,22 @@ class Token {
       : type(type), text(text), value(value) {}
 };
 
-void parse(const std::string_view &input, std::vector<Token> &tokens) {
+static void parse(const std::string_view &input,
+                  std::vector<Token> &outTokens) {
   if (input.starts_with("mul")) {
-    tokens.emplace_back(Token::Type::MUL, "mul");
-    parse(input.substr(3), tokens);
+    outTokens.emplace_back(Token::Type::MUL, "mul");
+    parse(input.substr(3), outTokens);
   } else if (input.starts_with("(")) {
-    tokens.emplace_back(Token::Type::PAREN_OPEN, "(");
-    parse(input.substr(1), tokens);
+    outTokens.emplace_back(Token::Type::PAREN_OPEN, "(");
+    parse(input.substr(1), outTokens);
   } else if (input.starts_with(")")) {
-    tokens.emplace_back(Token::Type::PAREN_CLOSE, ")");
-    parse(input.substr(1), tokens);
+    outTokens.emplace_back(Token::Type::PAREN_CLOSE, ")");
+    parse(input.substr(1), outTokens);
   } else if (input.starts_with(",")) {
-    tokens.emplace_back(Token::Type::COMMA, ",");
-    parse(input.substr(1), tokens);
+    outTokens.emplace_back(Token::Type::COMMA, ",");
+    parse(input.substr(1), outTokens);
   } else if (!input.empty()) {
     if (std::isdigit(*input.begin())) {
-      int value{};
       size_t i = 0;
       for (; i < std::min(input.length(), size_t(3)); i++) {
         if (!std::isdigit(input.at(i))) {
@@ -50,18 +52,67 @@ void parse(const std::string_view &input, std::vector<Token> &tokens) {
         }
       }
 
-      tokens.emplace_back(Token::Type::VALUE, input.substr(0, i), value);
-      parse(input.substr(i), tokens);
+      int value = std::stod(input.substr(0, i).data());
+      outTokens.emplace_back(Token::Type::VALUE, input.substr(0, i), value);
+      parse(input.substr(i), outTokens);
     } else {
-      tokens.emplace_back(Token::Type::UNKNOWN, *input.begin());
-      parse(input.substr(1), tokens);
+      outTokens.emplace_back(Token::Type::UNKNOWN, *input.begin());
+      parse(input.substr(1), outTokens);
     }
   }
 }
 
+static void lex(std::span<Token> tokens,
+                std::vector<std::pair<int, int>> &outMuls) {
+  if (tokens.size() < 5) {
+    return;
+  }
+
+  if (tokens.begin()->type != Token::Type::MUL) {
+    lex(tokens.subspan(1), outMuls);
+    return;
+  }
+
+  if (tokens[1].type != Token::Type::PAREN_OPEN) {
+    lex(tokens.subspan(2), outMuls);
+    return;
+  }
+
+  if (tokens[2].type != Token::Type::VALUE) {
+    lex(tokens.subspan(3), outMuls);
+    return;
+  }
+
+  int firstValue = tokens[2].value;
+
+  if (tokens[3].type != Token::Type::COMMA) {
+    lex(tokens.subspan(4), outMuls);
+    return;
+  }
+
+  if (tokens[4].type != Token::Type::VALUE) {
+    lex(tokens.subspan(5), outMuls);
+    return;
+  }
+
+  int secondValue = tokens[4].value;
+
+  if (tokens[5].type != Token::Type::PAREN_CLOSE) {
+    lex(tokens.subspan(6), outMuls);
+    return;
+  }
+
+  // we found a valid sequence!
+  outMuls.emplace_back(firstValue, secondValue);
+  lex(tokens.subspan(6), outMuls);
+}
+
 int main(int argc, char **argv) {
-  std::vector<Token> tokens;
+  std::vector<Token> tokens{};
   parse(input, tokens);
 
+  std::vector<std::pair<int, int>> muls{};
+  lex(tokens, muls);
+
   std::cout << "ok";
 }
\ No newline at end of file