Create shift-2d-grid.cpp

Author: kamyu104

C++/shift-2d-grid.cpp

@@ -0,0 +1,28 @@
+// Time:  O(m * n)
+// Space: O(1)
+
+class Solution {
+public:
+    vector<vector<int>> shiftGrid(vector<vector<int>>& grid, int k) {
+        rotate(&grid, k);
+        return grid;
+    }
+
+private:
+    void rotate(vector<vector<int>> *grid, int k) {
+        k %= grid->size() * (*grid)[0].size();
+        reverse(grid, 0, grid->size() * (*grid)[0].size());
+        reverse(grid, 0, k);
+        reverse(grid, k, grid->size() * (*grid)[0].size());
+    }
+    
+    void reverse(vector<vector<int>> *grid, int start, int end) {
+        for (; start < end; ++start, --end) {
+            int start_r = start / (*grid)[0].size();
+            int start_c = start % (*grid)[0].size();
+            int end_r = (end - 1) / (*grid)[0].size();
+            int end_c = (end - 1) % (*grid)[0].size();
+            swap((*grid)[start_r][start_c], (*grid)[end_r][end_c]);
+        }
+    }
+};