advent-of-code/2024/9/main-1.cpp
2024-12-08 22:53:26 -08:00

54 lines
899 B
C++

#include <bits/stdc++.h>
using namespace std;
typedef unsigned long long ull;
int main() {
ios::sync_with_stdio(0);
cin.tie(0);
char c;
deque<tuple<int, int, int>> blocks;
deque<tuple<int, int>> frees;
int i = 0, n = 0;
bool rfree = false;
while (cin >> c) {
c -= '0';
if (rfree) {
if (c > 0) {
frees.push_back({n, c});
}
} else {
blocks.push_back({i++, n, c});
}
rfree = !rfree;
n += c;
}
while (frees.size() > 0) {
auto &[bi, bx, bn] = blocks.back();
auto &[fx, fn] = frees[0];
if (fx > bx) {
break;
}
int nmoved = min(fn, bn);
bn -= nmoved;
fn -= nmoved;
blocks.push_front({bi, fx, nmoved});
if (fn == 0) {
frees.pop_front();
} else {
fx += nmoved;
}
if (bn == 0) {
blocks.pop_back();
}
}
ull sum = 0;
for (auto &[bi, bx, bn] : blocks) {
sum += (ull)bi * (bn * bx + bn * (bn - 1) / 2);
}
cout << sum << '\n';
}