Create 3531. Count Covered Buildings (#955)

Author: Chayandas07

3531. Count Covered Buildings

@@ -0,0 +1,36 @@
+class Solution {
+public:
+    int countCoveredBuildings(int n, vector<vector<int>>& buildings) {
+        unordered_map<int, set<int>> rowToCol, colToRow;
+        for (auto &b : buildings) {
+            int x = b[0], y = b[1];
+            rowToCol[x].insert(y);
+            colToRow[y].insert(x);
+        }
+
+        int cnt = 0;
+        for (auto &b : buildings) {
+            int x = b[0], y = b[1];
+            auto &cols = rowToCol[x];
+            auto it = cols.lower_bound(y);
+            bool hasLeft = (it != cols.begin());
+            bool hasRight = false;
+            if (it != cols.end()) {
+                auto it2 = it; ++it2;
+                hasRight = (it2 != cols.end());
+            }
+
+            auto &rows = colToRow[y];
+            auto it3 = rows.lower_bound(x);
+            bool hasUp = (it3 != rows.begin());
+            bool hasDown = false;
+            if (it3 != rows.end()) {
+                auto it4 = it3; ++it4;
+                hasDown = (it4 != rows.end());
+            }
+
+            if (hasLeft && hasRight && hasUp && hasDown) cnt++;
+        }
+        return cnt;
+    }
+};