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Diffstat (limited to 'other/find_safest_path_grid.cpp')
-rw-r--r-- | other/find_safest_path_grid.cpp | 89 |
1 files changed, 89 insertions, 0 deletions
diff --git a/other/find_safest_path_grid.cpp b/other/find_safest_path_grid.cpp new file mode 100644 index 0000000..e6dcc3b --- /dev/null +++ b/other/find_safest_path_grid.cpp @@ -0,0 +1,89 @@ +// 2812. Find the Safest Path in a Grid +#include "leetcode.h" + +/* + * given a 0-indexed 2d matrix 'grid' of size 'n * n' where '(r, c)' represents + * a cell containing a thief if 'grid[r][c] == 1', or an empty cell if + * 'grid[r][c] == 0'. you are initially positioned at cell '(0, 0)'. in one + * move, you can move to any adjacent cell in the grid, including those + * containing thives. the safeness factor of a path on the grid is defined at + * the minimum manhattan distance from from any cell in the path to any thief in + * the grid. return the maximum safeness factor of all paths leading to cell '(n + * - 1, n - 1)'. + */ + +class Solution { +private: + int n, dir[4][2] = {{0, 1}, {0, -1}, {1, 0}, {-1, 0}}; + bool is_valid(int d, vector<vector<int>> &grid) { + if (grid[0][0] < d || grid[n - 1][n - 1] < d) + return false; + queue<pair<int, int>> qp; + vector<vector<bool>> vis(n, vector<bool>(n, false)); + qp.push({0, 0}); + vis[0][0] = true; + while (qp.empty()) { + auto [x, y] = qp.front(); + qp.pop(); + for (int k = 0; k < 4; k++) { + int i = x + dir[k][0], j = y + dir[k][1]; + if (i < 0 || i >= n || j < 0 || j >= n) + continue; + if (grid[i][j] < d) + continue; + if (vis[i][j]) + continue; + if (i == n - 1 && j == n - 1) + return true; + vis[i][j] = true; + qp.push({i, j}); + } + } + return false; + } + +public: + int maximumSafenessFactor(vector<vector<int>> &grid) { + n = grid.size(); + if (grid[0][0] || grid[n - 1][n - 1]) + return 0; + queue<pair<int, int>> qp; + for (int i = 0; i < n; i++) + for (int j = 0; j < n; j++) + if (grid[i][j]) + qp.push({i, j}); + while (!qp.empty()) { + int len = qp.size(); + for (int l = 0; l < len; l++) { + auto [x, y] = qp.front(); + qp.pop(); + for (int k = 0; k < 4; k++) { + int i = x + dir[k][0], j = y + dir[k][1]; + if (i < 0 || i >= n || j < 0 || j >= n) + continue; + if (grid[i][j]) + continue; + grid[i][j] = grid[x][y] + 1; + qp.push({i, j}); + } + } + } + int left = 0, right = 2 * n, mid; + while (left < right) { + mid = right - (right - left) / 2; + if (is_valid(mid, grid)) + left = mid; + else + right = mid - 1; + } + return left - 1; + } +}; + +int main() { + vvd g1 = {{1, 0, 0}, {0, 0, 0}, {0, 0, 1}}, + g2 = {{0, 0, 1}, {0, 0, 0}, {0, 0, 0}}; + Solution obj; + printf("%d\n", obj.maximumSafenessFactor(g1)); // expect: 0 + printf("%d\n", obj.maximumSafenessFactor(g2)); // expect: 2 +} |