Proof. If childCnt ≥ 2 : the children occupy at least two columns on the next row, so a horizontal line is needed to connect the leftmost to the rightmost child (rule 2).
Only‑if childCnt = 1 : the sole child is placed directly under the parent; the horizontal segment would have length zero and is omitted by the drawing convention. ∎ The number of strokes contributed by a node v is 338. FamilyStrokes
def main() -> None: data = sys.stdin.read().strip().split() if not data: return it = iter(data) n = int(next(it)) g = [[] for _ in range(n + 1)] for _ in range(n - 1): u = int(next(it)); v = int(next(it)) g[u].append(v) g[v].append(u) ∎ The number of strokes contributed by a
root = 1 stack = [(root, 0)] # (node, parent) internal = 0 horizontal = 0 0)] # (node
while stack: v, p = stack.pop() child_cnt = 0 for w in g[v]: if w == p: continue child_cnt += 1 stack.append((w, v)) if child_cnt: internal += 1 if child_cnt >= 2: horizontal += 1
internalCnt ← 0 // |I| horizontalCnt ← 0 // # childCount(v) ≥ 2