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Diffstat (limited to '17/day4/knights.cpp')
| -rw-r--r-- | 17/day4/knights.cpp | 91 |
1 files changed, 91 insertions, 0 deletions
diff --git a/17/day4/knights.cpp b/17/day4/knights.cpp new file mode 100644 index 0000000..784abfc --- /dev/null +++ b/17/day4/knights.cpp @@ -0,0 +1,91 @@ +#include <bits/stdc++.h> +using namespace std; +using ll = long long; +constexpr ll INF = 1e12; + +int dx[] = { 2, 1, -1, -2, -2, -1, 1, 2 }; +int dy[] = { 1, 2, 2, 1, -1, -2, -2, -1 }; +char A[101][101]; + +template<int V, class T = ll> class max_flow { + struct edge { + int t, rev; + T cap, f; + }; + vector<edge> adj[V]; + int dist[V]; + int ptr[V]; + bool bfs(int s, int t) { + memset(dist, -1, sizeof dist); + dist[s] = 0; + queue<int> q({ s }); + while (!q.empty() && dist[t] == -1) { + int n = q.front(); + q.pop(); + for (auto& e : adj[n]) { + if (dist[e.t] == -1 && e.cap != e.f) { + dist[e.t] = dist[n] + 1; + q.push(e.t); + } + } + } + return dist[t] != -1; + } + T augment(int n, T amt, int t) { + if (n == t) return amt; + for (; ptr[n] < adj[n].size(); ptr[n]++) { + edge& e = adj[n][ptr[n]]; + if (dist[e.t] == dist[n] + 1 && e.cap != e.f) { + T flow = augment(e.t, min(amt, e.cap - e.f), t); + if (flow != 0) { + e.f += flow; + adj[e.t][e.rev].f -= flow; + return flow; + } + } + } + return 0; + } +public: + void add(int u, int v, T cap = 1, T rcap=0) { + adj[u].push_back({ v, (int) adj[v].size(), cap, 0 }); + adj[v].push_back({ u, (int) adj[u].size() - 1, rcap, 0 }); + } + T calc(int s, int t) { + T flow = 0; + while (bfs(s, t)) { + memset(ptr, 0, sizeof ptr); + while (T df = augment(s, INF, t)) flow += df; + } + return flow; + } + void clear() { + for (int n = 0; n < V; n++) adj[n].clear(); + } +}; + +int main() { + int R, C; + cin >> R >> C; + int ans = R * C; + for (int i = 0; i < R; ++i) { + for (int j = 0; j < C; ++j) cin >> A[i][j]; + } + + max_flow<101*101> MF; + for (int i = 0; i < R; ++i) { + for (int j = 0; j < C; ++j) { + if (A[i][j] == '#') { --ans; continue; } + if (i + j & 1) { + MF.add(10000, i * C + j, (A[i][j] == 'C' ? INF : 1)); + for (int d = 0; d < 8; ++d) { + int x = i + dx[d], y = j + dy[d]; + if (x < 0 || x >= R || y < 0 || y >= C || A[x][y] == '#') continue; + MF.add(i * C + j, x * C + y, INF); + } + } + else MF.add(i * C + j, 10001, (A[i][j] == 'C' ? INF : 1)); + } + } + cout << ans - MF.calc(10000, 10001) << '\n'; +}
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