This problem is in Contest(s) below:
Contest 1531:算法实验8
Contest 1744:【算法设计与分析】实验8 (区块链24-1、2+计算机24-5/6/9/10)
Contest 1745:【算法设计与分析】实验8 (计算机24-1/2)
Contest 1405:【算法设计与分析】实验8 回溯算法
Contest 1408:【算法设计与分析】实验八