Euler solved this problem in 1736. He changed this problem into the first graph theory problem by abstract analyzed method.
欧拉在1736年解决了这个问题，他用抽象分析法将这个问题化为第一个图论问题。
The crossing number of graph, which is an NP-complete problem, has an important theory meaning.
图的交叉数问题属于NP -困难问题，对它的研究有重要的理论意义。
In the last, the paper designs and analyses the Graph Theory algorithm and drives a conclusion that the problem of the arranging of curriculum schedule is NP - hard problem.
在文章的最后我们对课表超图的图论算法进行设计与分析，并得出该问题是一个NP难问题。
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