cpp: add «1463. Cherry Pickup II»

Signed-off-by: Matej Focko <me@mfocko.xyz>

cpp/cherry-pickup-ii.cpp

@@ -0,0 +1,83 @@
+#include <cassert>
+#include <vector>
+
+namespace {
+
+using grid_t = std::vector<std::vector<int>>;
+
+struct solver {
+    const int UNDEFINED = -1;
+
+    solver(const grid_t &grid)
+        : grid(grid), rows(static_cast<int>(grid.size())),
+          cols(static_cast<int>(grid[0].size())),
+          dp(rows, std::vector(cols, std::vector(cols, UNDEFINED))) {}
+
+    auto solve() -> int { return solve(0, 0, cols - 1); }
+
+  private:
+    const grid_t &grid;
+    int rows, cols;
+    std::vector<grid_t> dp;
+
+    auto contains(int y, int x) const -> bool {
+        return y >= 0 && y < rows && x >= 0 && x < cols;
+    }
+
+    auto solve(int y, int x0, int x1) -> int {
+        // out of bounds or same
+        if (!contains(y, x0) || !contains(y, x1) || x0 == x1) {
+            return 0;
+        }
+
+        // is memoized
+        if (dp[y][x0][x1] != UNDEFINED) {
+            return dp[y][x0][x1];
+        }
+
+        auto current = grid[y][x0] + grid[y][x1];
+
+        // last row
+        if (y == rows - 1) {
+            return current;
+        }
+
+        auto best = 0;
+        for (int d0 = -1; d0 <= 1; ++d0) {
+            for (int d1 = -1; d1 <= 1; ++d1) {
+                best = std::max(best, current + solve(y + 1, x0 + d0, x1 + d1));
+            }
+        }
+
+        dp[y][x0][x1] = best;
+        return best;
+    }
+};
+} // namespace
+
+class Solution {
+  public:
+    int cherryPickup(const std::vector<std::vector<int>> &grid) {
+        return solver(grid).solve();
+    }
+};
+
+int main() {
+    Solution s;
+
+    assert((s.cherryPickup(std::vector{
+                std::vector{3, 1, 1},
+                std::vector{2, 5, 1},
+                std::vector{1, 5, 5},
+                std::vector{2, 1, 1},
+            }) == 24));
+    assert((s.cherryPickup(std::vector{
+                std::vector{1, 0, 0, 0, 0, 0, 1},
+                std::vector{2, 0, 0, 0, 0, 3, 0},
+                std::vector{2, 0, 9, 0, 0, 0, 0},
+                std::vector{0, 3, 0, 5, 4, 0, 0},
+                std::vector{1, 0, 2, 3, 0, 0, 6},
+            }) == 28));
+
+    return 0;
+}