feat(1386_shift-2d-grid): add py3 soln

1386_shift-2d-grid/README.md

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+Given a 2D `grid` of size `m x n` and an integer `k`. You need to shift the `grid` `k` times.
+
+In one shift operation:
+
+*   Element at `grid[i][j]` moves to `grid[i][j + 1]`.
+*   Element at `grid[i][n - 1]` moves to `grid[i + 1][0]`.
+*   Element at `grid[m - 1][n - 1]` moves to `grid[0][0]`.
+
+Return the _2D grid_ after applying shift operation `k` times.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2019/11/05/e1.png)
+
+    Input: grid = [[1,2,3],[4,5,6],[7,8,9]], k = 1
+    Output: [[9,1,2],[3,4,5],[6,7,8]]
+    
+
+**Example 2:**
+
+![](https://assets.leetcode.com/uploads/2019/11/05/e2.png)
+
+    Input: grid = [[3,8,1,9],[19,7,2,5],[4,6,11,10],[12,0,21,13]], k = 4
+    Output: [[12,0,21,13],[3,8,1,9],[19,7,2,5],[4,6,11,10]]
+    
+
+**Example 3:**
+
+    Input: grid = [[1,2,3],[4,5,6],[7,8,9]], k = 9
+    Output: [[1,2,3],[4,5,6],[7,8,9]]
+    
+
+**Constraints:**
+
+*   `m == grid.length`
+*   `n == grid[i].length`
+*   `1 <= m <= 50`
+*   `1 <= n <= 50`
+*   `-1000 <= grid[i][j] <= 1000`
+*   `0 <= k <= 100`

1386_shift-2d-grid/python3/simulation.py

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+# Time: O(k · m · n)
+# Space: O(1)
+class Solution:
+    def shiftGrid(self, grid: List[List[int]], k: int) -> List[List[int]]:
+        # Simulation approach, we shift the 2D grid one time, k times
+        # This is acceptable for low values of k (given k <= 100)
+        rows, cols = len(grid), len(grid[0])
+        
+        for _ in range(k):
+            # Assume this is the first shift. When we finish shifting all
+            # elements, the first item in the resulting grid will be the
+            # last item from the original grid.
+            prev = grid[-1][-1]
+            
+            for i in range(rows):
+                for j in range(cols):
+                    tmp = grid[i][j]
+                    grid[i][j] = prev
+                    prev = tmp
+        
+        return grid