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