Initial commit

2020/puzzle-18-02.cc

@@ -0,0 +1,149 @@
+#include <algorithm>
+#include <array>
+#include <cassert>
+#include <iostream>
+#include <list>
+#include <map>
+#include <regex>
+#include <set>
+#include <string>
+#include <tuple>
+
+enum class Token : char {
+  Eof,
+  Number,
+  LParens = '(',
+  RParens = ')',
+  Add = '+',
+  Multiply = '*'
+};
+using Value = unsigned long;
+
+struct Parser {
+  Parser(std::string const &s) : expr_(s), pos_(0) { skip_whitespace(); }
+
+  Value evaluate() { return multop(); }
+
+private:
+  Value addop() {
+    auto value = primary();
+    do {
+      if (peek() == Token::Add) {
+        chew(Token::Add);
+        value += primary();
+      } else {
+        return value;
+      }
+    } while (true);
+  }
+
+  Value multop() {
+    auto value = addop();
+    do {
+      if (peek() == Token::Multiply) {
+        chew(Token::Multiply);
+        value *= addop();
+      } else {
+        return value;
+      }
+    } while (true);
+  }
+
+  Value primary() {
+    if (peek() == Token::LParens) {
+      chew(Token::LParens);
+      Value value = evaluate();
+      chew(Token::RParens);
+      return value;
+    } else if (peek() == Token::Number) {
+      return chew_number();
+    } else {
+      std::cout << "expr_ = " << expr_ << "\n";
+      std::cout << "pos_ = " << pos_ << "\n";
+      std::cout << "End = " << expr_.substr(pos_) << "\n";
+      assert(false);
+    }
+  }
+
+  Token peek() {
+    if (pos_ == expr_.size()) {
+      return Token::Eof;
+    }
+    switch (expr_[pos_]) {
+    case '(':
+      return Token::LParens;
+    case ')':
+      return Token::RParens;
+    case '+':
+      return Token::Add;
+    case '*':
+      return Token::Multiply;
+    case '-':
+    case '0':
+    case '1':
+    case '2':
+    case '3':
+    case '4':
+    case '5':
+    case '6':
+    case '7':
+    case '8':
+    case '9':
+      return Token::Number;
+    default:
+      std::cout << "expr_ = " << expr_ << "\n";
+      std::cout << "pos_ = " << pos_ << "\n";
+      std::cout << "End = " << expr_.substr(pos_) << "\n";
+      assert(false);
+    }
+  }
+
+  void chew(Token tok) {
+    assert(peek() == tok);
+    switch (tok) {
+    case Token::LParens:
+    case Token::RParens:
+    case Token::Add:
+    case Token::Multiply:
+      ++pos_;
+      skip_whitespace();
+      break;
+    default:
+      assert(false);
+    }
+  }
+
+  void skip_whitespace() {
+    while (pos_ < expr_.size() && expr_[pos_] == ' ') {
+      ++pos_;
+    }
+  }
+
+  Value chew_number() {
+    assert(peek() == Token::Number);
+
+    std::size_t len = 0;
+    Value value = std::stoul(expr_.substr(pos_), &len);
+    pos_ += len;
+    skip_whitespace();
+    return value;
+  }
+
+  std::string expr_;
+  std::string::size_type pos_;
+};
+
+int main(void) {
+  std::string line;
+  Value result = 0;
+  while (std::getline(std::cin, line)) {
+    Parser p(line);
+    Value r = p.evaluate();
+    std::cout << line << " = " << r << "\n";
+    result += r;
+  }
+
+  std::cout << "Sum: " << result << "\n";
+
+  return 0;
+}