Optimize day 9

d09.cc

@@ -12,12 +12,17 @@ struct map2d {
     unsigned height;
 };
 
+struct coord2d {
+    int y;
+    int x;
+};
+
 auto parse_input(char *file)
 {
     ifstream input(file);
     if (!input.is_open()) exit(1);
 
-    struct map2d map;
+    map2d map;
 
     unsigned width = 0;
     for (string line; getline(input, line);) {
@@ -33,7 +38,7 @@ auto parse_input(char *file)
     return map;
 }
 
-char getpoint2d(struct map2d input, int y, int x)
+char getpoint2d(map2d & input, int y, int x)
 {
     auto map = getmap2d(input);
     if (y < 0 || x < 0) return 9;
@@ -47,7 +52,7 @@ int surr[][2] = {
               { 1,  0},
 };
 
-bool is_lowest(struct map2d input, int y, int x)
+bool is_lowest(map2d & input, int y, int x)
 {
     char base = getpoint2d(input, y, x);
     for (int i = 0; i < 4; i++) {
@@ -57,23 +62,27 @@ bool is_lowest(struct map2d input, int y, int x)
     return true;
 }
 
-unsigned part1(auto input)
+unsigned part1(auto input, vector<coord2d> & lowpoints)
 {
-    unsigned lowpoints = 0;
-
     for (unsigned y = 0; y < input.height; y++) {
         for (unsigned x = 0; x < input.width; x++) {
             if (is_lowest(input, y, x)) {
-                char height = getpoint2d(input, y, x);
-                lowpoints += height + 1;
+                coord2d coord = {(int)y, (int)x};
+                lowpoints.push_back(coord);
             }
         }
     }
 
-    return lowpoints;
+    auto map = getmap2d(input);
+    unsigned total = 0;
+    for (coord2d coord : lowpoints) {
+        total += map[coord.y][coord.x] + 1;
+    }
+
+    return total;
 }
 
-unsigned recurse_basin(struct map2d input, unordered_set<unsigned> & basin, int y, int x)
+unsigned recurse_basin(map2d & input, unordered_set<unsigned> & basin, int y, int x)
 {
     if (basin.contains(y * input.width + x)) return 0;
     basin.insert(y * input.width + x);
@@ -85,24 +94,22 @@ unsigned recurse_basin(struct map2d input, unordered_set<unsigned> & basin, int
         int new_x = x + surr[i][1];
         char cmp = getpoint2d(input, new_y, new_x);
         if (cmp >= 9) continue;
-        if (cmp > base) size += recurse_basin(input, basin, new_y, new_x);
+        if (cmp >= base) size += recurse_basin(input, basin, new_y, new_x);
     }
     return size;
 }
 
-unsigned part2(auto input)
+uint64_t part2(auto input, vector<coord2d> lowpoints)
 {
     unsigned biggest[4] = {0};
 
-    for (unsigned y = 0; y < input.height; y++) {
-        for (unsigned x = 0; x < input.width; x++) {
-            unordered_set<unsigned> basin;
-            biggest[0] = recurse_basin(input, basin, y, x);
-            sort(biggest, biggest + 4);
-        }
+    for (coord2d coord : lowpoints) {
+        unordered_set<unsigned> basin;
+        biggest[0] = recurse_basin(input, basin, coord.y, coord.x);
+        sort(biggest, biggest + 4);
     }
 
-    return biggest[1] * biggest[2] * biggest[3];
+    return (uint64_t)biggest[1] * biggest[2] * biggest[3];
 }
 
 int main(int argc, char *argv[])
@@ -110,6 +117,7 @@ int main(int argc, char *argv[])
     if (argc <= 1) return 1;
     auto input = parse_input(argv[1]);
 
-    cout << part1(input) << endl;
-    cout << part2(input) << endl;
+    vector<coord2d> lowpoints;
+    cout << part1(input, lowpoints) << endl;
+    cout << part2(input, lowpoints) << endl;
 }