Create equal-row-and-column-pairs.cpp

Author: kamyu104

C++/equal-row-and-column-pairs.cpp

@@ -0,0 +1,41 @@
+// Time:  O(n^2)
+// Space: O(n^2)
+
+// hash table
+class Solution {
+public:
+    int equalPairs(vector<vector<int>>& grid) {
+        unordered_map<vector<int>, int, VectorHash<int>> cnt1;
+        for (const auto& row : grid) {
+            ++cnt1[row];
+        }
+        unordered_map<vector<int>, int, VectorHash<int>> cnt2;
+        for (int j = 0; j < size(grid[0]); ++j) {
+            vector<int> col(size(grid));
+            for (int i = 0; i < size(grid); ++i) {
+                col[i] = grid[i][j];
+            }
+            ++cnt2[col];
+        }
+        int result = 0;
+        for (const auto& [k, _] : cnt1) {
+            if (!cnt2.count(k)) {
+                continue;
+            }
+            result += cnt1[k] * cnt2[k];
+        }
+        return result;
+    }
+
+private:
+    template<typename T>
+    struct VectorHash {
+        size_t operator()(const std::vector<T>& v) const {
+            size_t seed = 0;
+            for (const auto& i : v) {
+                seed ^= std::hash<T>{}(i)  + 0x9e3779b9 + (seed<<6) + (seed>>2);
+            }
+            return seed;
+        }
+    };
+};