显然答案是关于 $K$ 的 $N-1$ 次多项式，DP 求出 $K=0,\ldots,N-1$ 的答案后插值即可，时间复杂度 $O(N^2)$。
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Discussion #1528 for Problem #17719. The Symbolic Tree
Type: Editorial
Status: Open
Posted by: jiangly
Posted at: 2026-04-15 16:04:14
Last updated: 2026-04-15 16:04:17
题解
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