From df4c18e47be4bef977e311bb427698b72d48b197 Mon Sep 17 00:00:00 2001
From: Eric Mertens <emertens@gmail.com>
Date: Tue, 4 Apr 2023 21:11:22 -0700
Subject: [PATCH] 21 working

---
 2022/21.cpp | 29 +++++++++++++----------------
 1 file changed, 13 insertions(+), 16 deletions(-)

diff --git a/2022/21.cpp b/2022/21.cpp
index 70a584a..54300a0 100644
--- a/2022/21.cpp
+++ b/2022/21.cpp
@@ -7,7 +7,6 @@
 #include <vector>
 
 #include <boost/phoenix.hpp>
-#include <boost/range/irange.hpp>
 #include <boost/spirit/include/qi.hpp>
 
 #include <doctest.h>
@@ -85,10 +84,10 @@ auto Parse(std::istream & in) -> Input
 }
 
 auto Eval(
-  std::unordered_map<std::string, std::int64_t> & values,
+  std::unordered_map<std::string, double> & values,
   std::unordered_map<std::string, Expr> const& exprs,
   std::string const& var)
-  -> std::int64_t
+  -> double
 {
   auto it = values.find(var);
   if (it != values.end()) {
@@ -97,7 +96,7 @@ auto Eval(
   auto const& [lhs,rhs,op] = exprs.at(var);
   auto const l = Eval(values, exprs, lhs);
   auto const r = Eval(values, exprs, rhs);
-  std::int64_t o;
+  double o;
   switch (op) {
     case Op::Add: o = l + r; break;
     case Op::Sub: o = l - r; break;
@@ -110,7 +109,7 @@ auto Eval(
 
 auto Part1(Input const& input) -> std::int64_t
 {
-  std::unordered_map<std::string, std::int64_t> values;
+  std::unordered_map<std::string, double> values;
   std::unordered_map<std::string, Expr> exprs;
   for (auto const& entry : input) {
     std::visit(overloaded {
@@ -123,7 +122,7 @@ auto Part1(Input const& input) -> std::int64_t
 
 auto Part2(Input const& input) -> std::int64_t
 {
-  std::unordered_map<std::string, std::int64_t> values;
+  std::unordered_map<std::string, double> values;
   std::unordered_map<std::string, Expr> exprs;
   for (auto const& entry : input) {
     std::visit(overloaded {
@@ -134,26 +133,24 @@ auto Part2(Input const& input) -> std::int64_t
 
   exprs.at("root").op = Op::Sub;
 
-  auto eval = [&](std::int64_t humn) -> std::int64_t {
+  auto eval = [&](double humn) -> double {
     auto values_ = values;
     values_.at("humn") = humn;
     return Eval(values_, exprs, "root");
   };
 
-  auto x0 = 10;
-  auto x1 = 20;
+  auto x0 = 10.0;
+  auto x1 = 20.0;
   auto fx0 = eval(x0);
-  auto fx1 = eval(x1);
-  std::int64_t a = 0, b = 1;
-  while (x0 != x1 || a%b != 0) {
-    a = eval(x1) * (x1 - x0);
-    b = eval(x1) - eval(x0);
-    auto const x2 = x1 - a / b;
+  while (std::abs(x0 - x1) > 0.01) {
+    auto const fx1 = eval(x1);
+    auto const x2 = x1 - fx1 * (x1 - x0) / (fx1 - fx0);
     x0 = x1;
     x1 = x2;
+    fx0 = fx1;
   }
 
-  return x0;
+  return std::round(x1);
 }
 
 } // namespace