spiral matrix ii

0059_spiral-matrix-ii/README.md

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+Given a positive integer `n`, generate an `n x n` `matrix` filled with elements from `1` to `n2` in spiral order.
+
+**Example 1:**
+
+![](https://assets.leetcode.com/uploads/2020/11/13/spiraln.jpg)
+
+    Input: n = 3
+    Output: [[1,2,3],[8,9,4],[7,6,5]]
+    
+
+**Example 2:**
+
+    Input: n = 1
+    Output: [[1]]
+    
+
+**Constraints:**
+
+*   `1 <= n <= 20`

0059_spiral-matrix-ii/python3/amols_approach.py

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+class Solution:
+    def generateMatrix(self, n: int) -> List[List[int]]:
+        if n==0: return []
+        if n==1: return [[1]]
+        
+        matrix = [[0]*n for _ in range(n)]
+        counter = 1
+    
+        rows, cols = n, n
+        top, down = 0, rows-1
+        left, right = 0, cols-1
+        dir = 0
+        
+        while top<=down and left<=right:
+            if dir==0:
+                for i in range(left, right+1):
+                    matrix[top][i] = counter
+                    counter+=1
+                top+=1
+                
+            elif dir==1:
+                for i in range(top, down+1):
+                    matrix[i][right] = counter
+                    counter+=1
+                right-=1
+                
+            elif dir==2:
+                for i in range(right, left-1, -1):
+                    matrix[down][i] = counter
+                    counter += 1
+                down-=1
+                
+            elif dir==3:
+                for i in range(down, top-1, -1):
+                    matrix[i][left] = counter
+                    counter += 1
+                left+=1
+        
+            dir = (dir+1)%4
+        
+        return matrix

0059_spiral-matrix-ii/python3/solution.py

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+import math
+
+class Solution:
+    def generateMatrix(self, n: int) -> List[List[int]]:
+        m = [[None] * n for _ in range(n)]
+        val = 1
+        
+        for i in range(math.ceil(n / 2)):
+            # Top
+            ri, ci = i, i
+            while ci < n - i:
+                m[ri][ci] = val
+                val += 1
+                ci += 1
+            ci -= 1
+            
+            # Right
+            ri, ci = ri + 1, ci
+            while ri < n - i:
+                m[ri][ci] = val
+                val += 1
+                ri += 1
+            ri -= 1
+            
+            # Bottom
+            ri, ci = ri, ci - 1
+            while ci >= i:
+                m[ri][ci] = val
+                val += 1
+                ci -= 1
+            ci += 1
+            
+            # Left
+            ri, ci = ri - 1, ci
+            while ri > i:
+                m[ri][ci] = val
+                val += 1
+                ri -= 1
+        
+        return m