Added solution for Spiral Matrix II.

anxious-coder-lhs · anxious-coder-lhs · commit 5a34c851ba5b · 2020-11-06T16:38:15.000+05:30
diff --git a/README.md b/README.md
@@ -54,6 +54,9 @@ Happy to accept any contributions to this in any langugage.
 19. [Leet Code 22 Generate Paranthesis](https://leetcode.com/problems/generate-parentheses/) | [Solution Brute Force](level_medium/LeetCode_22_Generate_Paranthesis_1.ts) | [Solution BF Optimized](level_medium/LeetCode_22_Generate_Paranthesis_2.ts)
 20. [Leet Code 54 Spiral Matrix](https://leetcode.com/problems/spiral-matrix/) | [Solution](./med/../level_medium/SpiralMatrix.ts)
 21. [Leet Code 1239 - Maximum length of the unique character string](https://leetcode.com/problems/maximum-length-of-a-concatenated-string-with-unique-characters/) | [Solution](./level_medium/LeetCode_1239_MaxLength.ts)
+22. [Leet Code 445 - Add Numbers II](https://leetcode.com/problems/add-two-numbers-ii/) | [Solution 1](./level_medium/LeetCode%20445_Add%202%20Numbers_1.ts) | [Solution 2](./level_medium/LeetCode%20445_Add%202%20Numbers_2.ts)
+23. [Leet Code 59 - Spiral Matrix II](https://leetcode.com/problems/spiral-matrix-ii/) | [Solution](level_medium/SpiralMatrixII.ts)
+
 
 
 ## Hard
@@ -62,8 +65,7 @@ Happy to accept any contributions to this in any langugage.
 3. [Leet Code 297 - Serialize Deserialize Binary Tree](https://leetcode.com/problems/serialize-and-deserialize-binary-tree/) | [Solution](./level_hard/SerializeDeserializeBinaryTree.ts)
 4. [Leet Code 428 - Serialize Deserialize N-Ary Tree](https://leetcode.com/problems/serialize-and-deserialize-n-ary-tree/) | [Solution](./level_hard/SerializeDeserializeNAryTree.ts)
 5. [Leet Code 25 - Reverse Linked List k Nodes at a time](https://leetcode.com/problems/reverse-nodes-in-k-group/) | [Solution](./level_hard/LeetCode%2025_Reverse%20Linked%20List%20K%20Nodes.ts)
-6. [Leet Code 445 - Add Numbers II](https://leetcode.com/problems/add-two-numbers-ii/) | [Solution 1](./level_medium/LeetCode%20445_Add%202%20Numbers_1.ts) | [Solution 2](./level_medium/LeetCode%20445_Add%202%20Numbers_2.ts)
-
+   
 ## Sorting
 1. Bubble Sort | [Solution](./sorting/Sort_Bubble.js)
 2. Insertion Sort | [Solution](./sorting/Sort_Insertion.js)
diff --git a/level_medium/SpiralMatrixII.ts b/level_medium/SpiralMatrixII.ts
@@ -0,0 +1,53 @@
+/**
+ * Leet Code 59: Spiral Matrix II
+ * 
+ * Two Solutions are available:
+ *  Just like the Spiral Matrix I, we fill the items layer by layer by setting the perimeter boundaries to extremes.
+ * Then, we move in each direction, horizontal top, vertical right, horizontal bottom, vertical left and so on. After
+ * completing each layer, we squeeze the perimter boundary one by one, until we get to an invalid.
+ * 
+ *  2nd solution used here uses the directionality matrix which allows us to change the direction with each iteration.
+ * This allows us to use one loop till all the items are done. At each step, we need to change the direction of 
+ * the pivot to either left, bottom, right, or top. This can be done as we hit the wall.
+ * 
+ * Time: O(n*n) since each position needs to be visited once. Space: O(1) since no additional space is used apart
+ * from the result.
+ * 
+ * @param n 
+ */
+function generateMatrix(n: number): number[][] {
+    const result: number[][] = Array.from({length: n}, () => Array(n).fill(undefined));
+    let [row, col] = [0, 0], counter = 1, dIdx = 0;
+    while(true) {
+        result[row][col] =  counter++;
+        let [newRow, newCol] = getNextIdx(row, col, dIdx);
+        if (!isValidIdx(newRow, newCol, n) || isOccupied(result, newRow, newCol)) {
+            // Update the direction
+            dIdx = (dIdx + 1) % 4;
+            [newRow, newCol] = getNextIdx(row, col, dIdx);
+            
+            // Check if all items are filled.
+            if (!isValidIdx(newRow, newCol, n) || isOccupied(result, newRow, newCol)) break;
+        }
+        
+        row = newRow; col = newCol;
+    }
+    
+    return result;
+};
+
+function isValidIdx(row: number, col: number, max: number) {
+    return row >= 0 && row < max && col >= 0 && col < max;
+}
+
+function isOccupied(result: number[][], row: number, col: number) {
+    return result[row][col] !== undefined;
+}
+
+function getNextIdx(row: number, col: number, dIdx: number): number[] {
+    const directions: number[][] = [
+        [0, 1], [1, 0], [0, -1], [-1, 0]
+    ];
+    const direction = directions[dIdx];
+    return [row + direction[0], col + direction[1]]
+}
