LibreOJ: 2068

「SDOI2016」探险路线

Author: Macesuted

LibreOJ/2068.cpp

@@ -0,0 +1,91 @@
+/**
+ * @file 2068.cpp
+ * @author Macesuted ([email protected])
+ * @date 2022-12-07
+ *
+ * @copyright Copyright (c) 2022
+ *
+ */
+
+#include <bits/stdc++.h>
+using namespace std;
+
+#ifndef LOCAL
+#define endl '\n'
+#endif
+
+bool mem1;
+
+#define maxn 805
+
+int64_t a[maxn][maxn], sum[maxn][maxn], fl[maxn][maxn], fr[maxn][maxn], gl[maxn][maxn], gr[maxn][maxn], h[maxn][2];
+
+int64_t _(int xl, int xr, int yl, int yr) { return sum[xr][yr] - sum[xl - 1][yr] - sum[xr][yl - 1] + sum[xl - 1][yl - 1]; }
+int64_t dp(int n, int m) {
+    for (int i = 1; i <= n; i++)
+        for (int j = 1; j <= m; j++) sum[i][j] = sum[i][j - 1] + a[i][j];
+    for (int i = 1; i <= n; i++)
+        for (int j = 1; j <= m; j++) sum[i][j] += sum[i - 1][j];
+    for (int i = 0; i <= n + 1; i++)
+        for (int j = 0; j <= m + 1; j++) fl[i][j] = fr[i][j] = gl[i][j] = gr[i][j] = -1e18;
+    fl[1][1] = fr[1][1] = a[1][1], gl[n][m] = gr[n][m] = a[n][m];
+    for (int i = 1; i <= n; i++)
+        for (int j = 1 + (i == 1); j <= m; j++)
+            fl[i][j] = max({fl[i][j - 1], fl[i - 1][j] + a[i][1], fr[i - 1][j - 1] + _(i, i, 1, j) + _(1, i - 1, j, j)}),
+            fr[i][j] = max({fr[i - 1][j], fr[i][j - 1] + a[1][j], fl[i - 1][j - 1] + _(i, i, 1, j) + _(1, i - 1, j, j)});
+    for (int i = n; i; i--)
+        for (int j = m - (i == n); j; j--)
+            gl[i][j] = max({gl[i + 1][j], gl[i][j + 1] + a[n][j], gr[i + 1][j + 1] + _(i, i, j, m) + _(i + 1, n, j, j)}),
+            gr[i][j] = max({gr[i][j + 1], gr[i + 1][j] + a[i][n], gl[i + 1][j + 1] + _(i, i, j, m) + _(i + 1, n, j, j)});
+    int64_t ans = 0;
+    for (int i = 1; i <= n; i++) h[i][0] = fl[i][m], h[i][1] = -1e18;
+    for (int j = 1; j <= m; j++) {
+        int64_t val = -1e18;
+        for (int i = 1; i <= n; i++) {
+            val = max(val + a[i][m], _(1, i, j, j) + _(i, i, j + 1, m));
+            h[i][1] = max(h[i][1], (j == 1 ? 0 : fr[i][j - 1]) + val);
+        }
+    }
+    for (int i = 2; i <= n; i++)
+        h[i][0] = max({h[i][0], h[i - 1][0] + a[i][1], h[i - 1][1] + _(i, i, 1, m)}),
+        h[i][1] = max({h[i][1], h[i - 1][1] + a[i][m], h[i - 1][0] + _(i, i, 1, m)});
+    ans = max(ans, h[n][1]);
+    for (int i = 1; i <= n; i++) ans = max(ans, h[i - 1][1] + gr[i][m]);
+    for (int j = 1; j <= m; j++) {
+        int64_t val = -1e18;
+        for (int i = n; i; i--) {
+            val = max(val + a[i][1], _(i, n, j, j) + _(i, i, 1, j - 1));
+            ans = max(ans, h[i - 1][0] + (j == m ? 0 : gl[i][j + 1]) + val);
+        }
+    }
+    return ans;
+}
+
+void solve(void) {
+    int n, m;
+    cin >> n >> m;
+    for (int i = 1; i <= n; i++)
+        for (int j = 1; j <= m; j++) cin >> a[i][j];
+    int64_t ans = dp(n, m);
+    for (int i = 1; i <= max(n, m); i++)
+        for (int j = 1; j < i; j++) swap(a[i][j], a[j][i]);
+    cout << max(ans, dp(m, n)) << endl;
+    return;
+}
+
+bool mem2;
+
+int main() {
+    ios::sync_with_stdio(false), cin.tie(nullptr);
+#ifdef LOCAL
+    cerr << "Memory Cost: " << abs(&mem1 - &mem2) / 1024. / 1024. << "MB" << endl;
+#endif
+
+    int _ = 1;
+    while (_--) solve();
+
+#ifdef LOCAL
+    cerr << "Time Cost: " << clock() * 1000. / CLOCKS_PER_SEC << "MS" << endl;
+#endif
+    return 0;
+}