match earliest

3 files changed, 45 insertions, 10 deletions

diff --git a/src/2019/day3/README.md b/src/2019/day3/README.md
index 1b94596..1b1c05d 100644
--- a/src/2019/day3/README.md
+++ b/src/2019/day3/README.md
@@ -39,4 +39,31 @@ R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
 U98,R91,D20,R16,D67,R40,U7,R15,U6,R7 = distance 135
 What is the Manhattan distance from the central port to the closest intersection?
 
+--- Part Two ---
+It turns out that this circuit is very timing-sensitive; you actually need to minimize the signal delay.
 
+To do this, calculate the number of steps each wire takes to reach each intersection; choose the intersection where the sum of both wires' steps is lowest. If a wire visits a position on the grid multiple times, use the steps value from the first time it visits that position when calculating the total value of a specific intersection.
+
+The number of steps a wire takes is the total number of grid squares the wire has entered to get to that location, including the intersection being considered. Again consider the example from above:
+
+...........
+.+-----+...
+.|.....|...
+.|..+--X-+.
+.|..|..|.|.
+.|.-X--+.|.
+.|..|....|.
+.|.......|.
+.o-------+.
+...........
+In the above example, the intersection closest to the central port is reached after 8+5+5+2 = 20 steps by the first wire and 7+6+4+3 = 20 steps by the second wire for a total of 20+20 = 40 steps.
+
+However, the top-right intersection is better: the first wire takes only 8+5+2 = 15 and the second wire takes only 7+6+2 = 15, a total of 15+15 = 30 steps.
+
+Here are the best steps for the extra examples from above:
+
+R75,D30,R83,U83,L12,D49,R71,U7,L72
+U62,R66,U55,R34,D71,R55,D58,R83 = 610 steps
+R98,U47,R26,D63,R33,U87,L62,D20,R33,U53,R51
+U98,R91,D20,R16,D67,R40,U7,R15,U6,R7 = 410 steps
+What is the fewest combined steps the wires must take to reach an intersection?
diff --git a/src/2019/day3/aoc.cpp b/src/2019/day3/aoc.cpp
index a81a29f..967863a 100644
--- a/src/2019/day3/aoc.cpp
+++ b/src/2019/day3/aoc.cpp
@@ -27,7 +27,22 @@ void match(const std::vector<wire::line>& lhs, const std::vector<wire::line>& lv
   }
 }
 
-int day3(line_view file) {
+int match_closest(wire ws[]) {
+  day3point p1;
+  day3point p2;
+  ws[0].sort();
+  ws[1].sort();
+  match(ws[0].psh, ws[1].psv, &p1);
+  match(ws[1].psh, ws[0].psv, &p2);
+  day3point p = std::min(p1, p2);
+  return p.distance() ;
+}
+
+int match_earliest(wire ws[]) {
+  return 0;
+}
+
+std::pair<int, int> day3(line_view file) {
   wire ws[2];
   day3point mp{0, 0};
   int i{0};
@@ -36,14 +51,7 @@ int day3(line_view file) {
     ws[i++].parse(lv, &cp, &mp);
     return true;
   });
-  ws[0].sort();
-  ws[1].sort();
-  day3point p1;
-  day3point p2;
-  match(ws[0].psh, ws[1].psv, &p1);
-  match(ws[1].psh, ws[0].psv, &p2);
-  day3point p = std::min(p1, p2);
-  return p.distance() ;
+  return {match_earliest(ws), match_closest(ws)};
 }
 
 } // namespace aoc2019
diff --git a/src/2019/day3/aoc.h b/src/2019/day3/aoc.h
index 48b6812..41be5ed 100644
--- a/src/2019/day3/aoc.h
+++ b/src/2019/day3/aoc.h
@@ -107,6 +107,6 @@ struct wire {
   }
 };
 
-int day3(line_view);
+std::pair<int,int> day3(line_view);
 
 } // namespace aoc2019