正在初始化 std::memset

Question

我正在使用 std::memset 解决此处复制的 LeetCode problem。目前，map_cherries已被初始化为：

map_cherries[70][70][70] = {}
...
std::memset(map_cherries, -1, sizeof(map_cherries));

有没有办法同时设置 map_cherries 的维度和值，或者可能有任何 better/alternative 方法来做到这一点？谢谢！

问题

Given a rows x cols matrix grid representing a field of cherries. Each cell in grid represents the number of cherries that you can collect.

You have two robots that can collect cherries for you, Robot #1 is located at the top-left corner (0,0), and Robot #2 is located at the top-right corner (0, cols-1) of the grid.

Return the maximum number of cherries collection using both robots by following the rules below:

From a cell (i,j), robots can move to cell (i+1, j-1) , (i+1, j) or (i+1, j+1).

When any robot is passing through a cell, It picks it up all cherries, and the cell becomes an empty cell (0).

When both robots stay on the same cell, only one of them takes the cherries.

Both robots cannot move outside of the grid at any moment.

Both robots should reach the bottom row in the grid.

Example 1:

Input: grid = [[3,1,1],[2,5,1],[1,5,5],[2,1,1]]
Output: 24

Explanation: Path of robot #1 and #2 are described in color green and blue respectively.
Cherries taken by Robot #1, (3 + 2 + 5 + 2) = 12.

Cherries taken by Robot #2, (1 + 5 + 5 + 1) = 12. Total of cherries: 12 + 12 = 24.

Example 2:

Input: grid = [[1,0,0,0,0,0,1],[2,0,0,0,0,3,0],[2,0,9,0,0,0,0],[0,3,0,5,4,0,0],[1,0,2,3,0,0,6]]

Output: 28

Explanation: Path of robot #1 and #2 are described in color green and blue respectively.
Cherries taken by Robot #1, (1 + 9 + 5 + 2) = 17.

Cherries taken by Robot #2, (1 + 3 + 4 + 3) = 11.

Total of cherries: 17 + 11 = 28.

Constraints:

rows == grid.length

cols == grid[i].length

2 <= rows, cols <= 70

0 <= grid[i][j] <= 100

尝试

#include <cstdint>
#include <vector>
#include <cstring>

struct Solution {
    int map_cherries[70][70][70] = {};

    int cherryPickup(std::vector<std::vector<int>>& grid) {
        std::memset(map_cherries, -1, sizeof(map_cherries));
        const std::size_t row_length = grid.size();
        const std::size_t col_length = grid[0].size();
        return depth_first_search(grid, row_length, col_length, 0, 0, col_length - 1);
    }

private:
    int depth_first_search(
        std::vector<std::vector<int>>& grid,
        const std::size_t row_length,
        const std::size_t col_length,
        int row,
        int left_robot,
        int right_robot
    ) {
        if (row == row_length) {
            return 0;
        }

        if (map_cherries[row][left_robot][right_robot] != -1) {
            return map_cherries[row][left_robot][right_robot];
        }

        int max_cherries = 0;

        for (int left = -1; left < 2; left++) {
            for (int right = -1; right < 2; right++) {
                const int curr_left_robot = left_robot + left;
                const int curr_right_robot = right_robot + right;

                if (curr_left_robot > -1 and curr_left_robot < col_length and curr_right_robot > -1 and curr_right_robot < col_length) {
                    max_cherries = std::max(max_cherries, depth_first_search(
                                                grid,
                                                row_length,
                                                col_length,
                                                row + 1,
                                                curr_left_robot,
                                                curr_right_robot
                                            ));
                }
            }
        }

        int total_cherries = grid[row][left_robot];

        if (left_robot != right_robot) {
            total_cherries += grid[row][right_robot];
        }

        total_cherries += max_cherries;
        return map_cherries[row][left_robot][right_robot] = total_cherries;
    }
};

输入

[[3,1,1],[2,5,1],[1,5,5],[2,1,1]]
[[1,0,0,3],[0,0,0,3],[0,0,3,3],[9,0,3,3]]
[[1,10,0,3,86,40],[0,0,0,3,86,40],[0,0,3,3,86,40],[9,0,3,3,86,40], [1,0,40,3,86,40],[0,22,0,3,86,40],[99,0,3,3,86,40],[9,0,3,3,86,40]]

产出

24
22
819

参考资料

Answer 1

一种方法是这样的：

auto map_cherries = std::vector(70, std::vector(70, std::vector(70, -1)));

只能从 c++17 开始使用。

正在初始化 std::memset

Initializing std::memset

c++

memset

c++17

问题

Constraints:

尝试

输入

产出

参考资料