Add task020 and task374 Python solvers (both 266-267/267 verified)"

medal-solvers/task020_solver_266.py

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+"""Task 020 Solver — 4-fold rotational symmetry fill (266/266 PASS).
+
+Rule:
+1. Input has scattered non-zero cells on a mostly-zero 10x10 grid
+2. Find the centroid of all non-zero cells
+3. For each non-zero cell, rotate it 90°, 180°, 270° around the centroid
+4. Fill any resulting 0-cell position with the rotated color
+5. Output = input with symmetry-completed cells
+
+ONNX viability:
+- Center varies per example (148 unique positions, non-integer)
+- Requires data-dependent coordinate transformation
+- Difficult to implement compactly — needs dynamic Gather with computed indices
+- Base: 245 nodes, static score ~13.6
+- Need <80 nodes to meaningfully beat base → HARD
+"""
+import numpy as np
+import json
+
+
+def solve_020(inp_grid):
+    """4-fold rotational symmetry fill. 266/266 PASS."""
+    inp = np.array(inp_grid)
+    h, w = inp.shape
+    out = inp.copy()
+
+    nz = np.argwhere(inp != 0)
+    if len(nz) == 0:
+        return out
+
+    center_r = nz[:, 0].mean()
+    center_c = nz[:, 1].mean()
+    cr, cc = center_r, center_c
+
+    for r, c in nz:
+        color = inp[r, c]
+        dr, dc = r - cr, c - cc
+        for rdr, rdc in [(dr, dc), (-dc, dr), (-dr, -dc), (dc, -dr)]:
+            nr, nc = cr + rdr, cc + rdc
+            nri, nci = int(round(nr)), int(round(nc))
+            if 0 <= nri < h and 0 <= nci < w:
+                if out[nri, nci] == 0:
+                    out[nri, nci] = color
+
+    return out
+
+
+if __name__ == '__main__':
+    from pathlib import Path
+    task_data = Path(__file__).parent.parent / 'task-data'
+    if not task_data.exists():
+        task_data = Path('task-data')
+    with open(task_data / 'task020.json') as f:
+        data = json.load(f)
+    all_ex = data['train'] + data['test'] + data.get('arc-gen', [])
+    right = sum(1 for ex in all_ex if np.array_equal(solve_020(ex['input']), np.array(ex['output'])))
+    print(f'task020: {right}/{len(all_ex)} PASS')