Create 2812. Find the Safest Path in a Grid1 (#479)

Author: Chayandas07

2812. Find the Safest Path in a Grid1

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+class Solution {
+public:
+    int n;
+    // Check if coordinates are valid within the grid boundaries
+    bool valid(int i, int j) {
+        return (i >= 0 && i < n && j >= 0 && j < n);
+    }
+    // Check if coordinates are valid within the grid boundaries
+    bool isValid(int x, int y, int n) {
+        return x >= 0 && x < n && y >= 0 && y < n;
+    }
+
+    // Function to compute the minimum distance grid
+    vector<vector<int>> computeDistanceGrid(vector<vector<int>>& grid) {
+        int n = grid.size();
+        vector<vector<int>> distGrid(n, vector<int>(n, INT_MAX)); // Initialize with maximum value
+        queue<pair<int, int>> q;
+
+        // Initialize the queue and distance for '0' cells
+        for (int i = 0; i < n; ++i) {
+            for (int j = 0; j < n; ++j) {
+                if (grid[i][j] == 1) {
+                    q.push({i, j});
+                    distGrid[i][j] = 0;
+                }
+            }
+        }
+
+        // Directions: up, down, left, right
+        vector<pair<int, int>> directions = {{-1, 0}, {1, 0}, {0, -1}, {0, 1}};
+
+        // BFS to compute minimum distances
+        while (!q.empty()) {
+            auto [x, y] = q.front();
+            q.pop();
+            for (auto& dir : directions) {
+                int newX = x + dir.first;
+                int newY = y + dir.second;
+                if (isValid(newX, newY, n) && distGrid[newX][newY] == INT_MAX) {
+                    distGrid[newX][newY] = distGrid[x][y] + 1;
+                    q.push({newX, newY});
+                }
+            }
+        }
+
+        return distGrid;
+    }
+
+    int maximumSafenessFactor(vector<vector<int>>& grid) {
+        n = grid.size();
+        if (grid[n - 1][n - 1] == 1 || grid[0][0] == 1) return 0;
+
+        vector<vector<int>> dist = computeDistanceGrid(grid);
+        priority_queue<pair<int, pair<int, int>>> pq;
+        vector<vector<int>> vis(n, vector<int>(n, 0));
+
+        vector<int> delr = {-1, 0, 1, 0};
+        vector<int> delc = {0, 1, 0, -1};
+
+        pq.push({dist[0][0], {0, 0}});
+        vis[0][0] = 1;
+
+        while (!pq.empty()) {
+            auto it = pq.top();
+            pq.pop();
+            int ds = it.first;
+            int i = it.second.first;
+            int j = it.second.second;
+
+            if (i == n - 1 && j == n - 1) return ds;
+
+            for (int l = 0; l < 4; ++l) {
+                int nrow = i + delr[l];
+                int ncol = j + delc[l];
+                if (valid(nrow, ncol) && grid[nrow][ncol] != 1 && !vis[nrow][ncol]) {
+                    vis[nrow][ncol] = 1;
+                    int ds1 = dist[nrow][ncol];
+                    pq.push({min(ds, ds1), {nrow, ncol}});
+                }
+            }
+        }
+
+        return 0;
+    }
+};