Create 2257. Count Unguarded Cells in the Grid

2257. Count Unguarded Cells in the Grid

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+char grid[100000];
+class Solution {
+public:
+    int m, n, comp;
+    int d[5] = {0, 1, 0, -1, 0};
+    inline int idx(int r, int c) { return r * n + c; }
+    inline void cross(int r, int c) {
+        for (int a = 0; a < 4; a++) {
+            int di = d[a], dj = d[a + 1];
+            for (int i = r + di, j = c + dj;; i += di, j += dj) {
+                int pos = idx(i, j);
+                if (i < 0 || i >= m || j < 0 || j >= n || grid[pos] == 'X')
+                    break;
+                comp -= (grid[pos] == ' ');
+                grid[pos] = 'V';
+            }
+        }
+    }
+
+    int countUnguarded(int m, int n, vector<vector<int>>& guards,
+                       vector<vector<int>>& walls) {
+        this->m = m, this->n = n;
+        comp = m * n;
+        memset(grid, ' ', m * n);
+
+        for (auto& ij : walls) {
+            grid[idx(ij[0], ij[1])] = 'X';
+            comp--;
+        }
+
+        for (auto& ij : guards) {
+            grid[idx(ij[0], ij[1])] = 'X';
+            comp--;
+        }
+
+        for (auto& ij : guards) {
+            cross(ij[0], ij[1]);
+        }
+        return comp;
+    }
+};