chore: import upstream snapshot with attribution

curriculum/challenges/english/blocks/daily-coding-challenges-python/6a22d77ddf034bc4e35b1d5d.md

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+---
+id: 6a22d77ddf034bc4e35b1d5d
+title: "Challenge 356: Magic Square Solver"
+challengeType: 29
+dashedName: challenge-356
+---
+
+# --description--
+
+Given a 3x3 grid with one missing number (represented as `0`), return the missing number that completes the magic square, or `"impossible"` if no valid number exists.
+
+A magic square is a grid where every row, column, and diagonal adds up to the same number.
+
+# --hints--
+
+`solve_magic_square([[2, 7, 6], [9, 0, 1], [4, 3, 8]])` should return `5`.
+
+```js
+({test: () => { runPython(`
+from unittest import TestCase
+TestCase().assertEqual(solve_magic_square([[2, 7, 6], [9, 0, 1], [4, 3, 8]]), 5)`)
+}})
+```
+
+`solve_magic_square([[0, 14, 12], [18, 10, 2], [8, 6, 16]])` should return `4`.
+
+```js
+({test: () => { runPython(`
+from unittest import TestCase
+TestCase().assertEqual(solve_magic_square([[0, 14, 12], [18, 10, 2], [8, 6, 16]]), 4)`)
+}})
+```
+
+`solve_magic_square([[12, 17, 16], [19, 0, 10], [14, 13, 18]])` should return `"impossible"`.
+
+```js
+({test: () => { runPython(`
+from unittest import TestCase
+TestCase().assertEqual(solve_magic_square([[12, 17, 16], [19, 0, 10], [14, 13, 18]]), "impossible")`)
+}})
+```
+
+`solve_magic_square([[15, 35, 31], [43, 27, 11], [23, 19, 0]])` should return `39`.
+
+```js
+({test: () => { runPython(`
+from unittest import TestCase
+TestCase().assertEqual(solve_magic_square([[15, 35, 31], [43, 27, 11], [23, 19, 0]]), 39)`)
+}})
+```
+
+`solve_magic_square([[26, 41, 14], [47, 35, 0], [32, 29, 44]])` should return `"impossible"`.
+
+```js
+({test: () => { runPython(`
+from unittest import TestCase
+TestCase().assertEqual(solve_magic_square([[26, 41, 14], [47, 35, 0], [32, 29, 44]]), "impossible")`)
+}})
+```
+
+# --seed--
+
+## --seed-contents--
+
+```py
+def solve_magic_square(grid):
+
+    return grid
+```
+
+# --solutions--
+
+```py
+def solve_magic_square(grid):
+    flat = [n for row in grid for n in row]
+    zero_index = flat.index(0)
+    row = zero_index // 3
+    col = zero_index % 3
+
+    target = next(sum(r) for r in grid if 0 not in r)
+
+    missing = target - sum(grid[row])
+    filled = [r[:] for r in grid]
+    filled[row][col] = missing
+
+    def check(arr):
+        return sum(arr) == target
+
+    for i in range(3):
+        if not check(filled[i]):
+            return "impossible"
+        if not check([filled[r][i] for r in range(3)]):
+            return "impossible"
+
+    if not check([filled[0][0], filled[1][1], filled[2][2]]):
+        return "impossible"
+    if not check([filled[0][2], filled[1][1], filled[2][0]]):
+        return "impossible"
+
+    return missing
+```