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#include <iostream>
#include <fstream>
#include <string>
#include <cerrno>
#include <vector>
#include <set>
#include <queue>
#include <algorithm>
using namespace std;
std::string get_file_contents(const char *filename)
{
std::ifstream in(filename, std::ios::in | std::ios::binary);
if (!in)
{
throw(errno);
}
std::string contents;
in.seekg(0, std::ios::end);
contents.resize(in.tellg());
in.seekg(0, std::ios::beg);
in.read(&contents[0], contents.size());
in.close();
return contents;
}
using heightmap_t = vector<vector<int>>;
heightmap_t parse_height_map(const char* input, int len){
vector<vector<int>> output;
vector<int> currRow;
for (int i = 0; i < len; i++) {
if (input[i] == '\n') {
output.push_back(currRow);
currRow = vector<int>();
} else {
currRow.push_back(input[i] - '0');
}
}
if (currRow.size() > 0) {
output.push_back(currRow);
}
return output;
}
bool isLowPoint(const heightmap_t &heightmap, int x, int y) {
int point = heightmap[y][x];
for (int dx = -1; dx < 2; dx++) {
for (int dy = -1; dy < 2; dy++) {
int checkX = x + dx;
int checkY = y + dy;
if ((checkX == x && checkY == y) ||
checkX < 0 || checkY < 0 ||
checkY >= heightmap.size() || checkX >= heightmap[checkY].size())
continue;
if (heightmap[checkY][checkX] <= point) {
return false;
}
}
}
return true;
}
struct coord {
int x;
int y;
coord(int x, int y) {
this->x = x;
this->y = y;
}
int hash() const {
return this->x << 16 | this->y;
}
bool operator==(const coord &a) const {
return a.x == x && a.y == y;
}
bool operator<(const coord &a) const {
return this->hash() < a.hash();
}
};
int findBasinSize(const heightmap_t &heightmap, int startX, int startY) {
set<coord> visited;
queue<coord> queue;
queue.emplace(startX, startY);
int totalSize = 0;
while(!queue.empty()) {
int x = queue.front().x;
int y = queue.front().y;
queue.pop();
if (x < 0 || y < 0 || y >= heightmap.size() || x >= heightmap[y].size() || heightmap[y][x] == 9 || visited.count({x, y})) {
continue;
}
totalSize++;
visited.insert({x, y});
for (int dx = -1; dx < 2; dx++) {
for (int dy = -1; dy < 2; dy++) {
int checkX = x + dx;
int checkY = y + dy;
if (dx != 0 && dy != 0) // dont allow diagonals / {x, y}
continue;
queue.emplace(checkX, checkY);
}
}
}
return totalSize;
}
int main() {
std::string input = get_file_contents("input");
auto heightmap = parse_height_map(input.c_str(), input.length());
int lowPointCount = 0;
int totalRisk = 0;
int topBasins[] = {0, 0, 0};
for (int y = 0; y < heightmap.size(); y++) {
for (int x = 0; x < heightmap[y].size(); x++) {
if (isLowPoint(heightmap, x, y)) {
lowPointCount++;
totalRisk += heightmap[y][x] + 1;
int basinSize = findBasinSize(heightmap, x, y);
for (int i = 0; i < 3; i++) {
if (topBasins[i] < basinSize) {
topBasins[i] = basinSize;
break;
}
}
sort(topBasins, topBasins + 3);
}
}
}
int acc = 1;
for (int i = 0; i < 3; i++) {
acc *= topBasins[i];
}
printf("Total low points: %d\n", lowPointCount);
printf("Total risk: %d\n", totalRisk);
printf("Part B answer: %d\n", acc);
}
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