bfs and direction

Author: henrytien

leetcode/317.shortest_distance_from_all_buildings/317.ShortestDistancefromAllBuildings_henrytien.cpp

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+// Source : https://leetcode.com/problems/shortest-distance-from-all-buildings/
+// Author : henrytien
+// Date   : 2022-02-05
+
+/*****************************************************************************************************
+ *
+ * You are given an m x n grid grid of values 0, 1, or 2, where:
+
+each 0 marks an empty land that you can pass by freely,
+each 1 marks a building that you cannot pass through, and
+each 2 marks an obstacle that you cannot pass through.
+You want to build a house on an empty land that reaches all buildings in the shortest total travel
+distance. You can only move up, down, left, and right.
+
+Return the shortest travel distance for such a house. If it is not possible to build such a house
+according to the above rules, return -1.
+
+The total travel distance is the sum of the distances between the houses of the friends and the meeting point.
+
+The distance is calculated using Manhattan Distance, where distance(p1, p2) = |p2.x - p1.x| + |p2.y - p1.y|.
+ ******************************************************************************************************/
+
+#include "../inc/ac.h"
+class Solution
+{
+public:
+    int shortestDistance(vector<vector<int>> &grid)
+    {
+        // Calculate every building point to landing point distance, and get the minm.
+        int m = grid.size(), n = grid[0].size();
+        vector<int> direction = {-1, 0, 1, 0, -1}; // left up right down
+        auto total = grid;
+        int min_dist = 0, walk = 0;
+        for (int i = 0; i < m; i++)
+        {
+            for (int j = 0; j < n; j++)
+            {
+                if (grid[i][j] == 1)
+                {
+                    min_dist = -1;
+                    auto dist = grid;
+                    queue<pair<int, int>> que;
+
+                    que.emplace(i, j);
+
+                    while (!que.empty())
+                    {
+                        auto land = que.front();
+                        que.pop();
+
+                        for (int k = 0; k < 4; k++)
+                        {
+                            int x = land.first + direction[k];
+                            int y = land.second + direction[k + 1];
+                            if (x >= 0 && x < m && y >= 0 && y < n && walk == grid[x][y])
+                            {
+                                grid[x][y]--;
+                                dist[x][y] = dist[land.first][land.second] + 1;
+                                total[x][y] += dist[x][y] - 1;
+                                que.emplace(x, y);
+                                if (min_dist < 0 || min_dist > total[x][y])
+                                {
+                                    min_dist = total[x][y];
+                                }
+                            }
+                        }
+                    }
+                    walk--;
+                }
+            }
+        }
+        return min_dist;
+    }
+};
+
+int main()
+{
+
+    vector<vector<int>> grid = {{1, 0, 2, 0, 1}, {0, 0, 0, 0, 0}, {0, 0, 1, 0, 0}};
+    cout << Solution().shortestDistance(grid) << "\n";
+    return 0;
+}

leetcode/317.shortest_distance_from_all_buildings/README.md

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+# [317. Shortest Distance from All Buildings](https://leetcode.com/problems/shortest-distance-from-all-buildings/)