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。
It belongs to NP complete problem in theory, so it's hard to solve in practical problems.
在理论上属于NP完全问题，在实际问题上很难解决。
The minimal vertex - covering problem of graph is a NP-complete problem of graph theory.
图的最小顶点覆盖问题是图论中的一个NP完全问题。
Because TSP is known to be a NP - complete problem in theory, it is too difficult to be solved with traditional optimal methods.
由于TSP问题在理论上属于NP完备问题，很难用一般的算法求解。
The security of these new cryptosystems depends on some NP-complete problems in the theory of Diophantine equations and on the difficulty of large number decomposition.
这些体制的安全性依赖于求解丢番图方程中的一些NP完全问题和大数的素因子分解的困难性。
Minimizing retransmission nodes in broadcasting is equivalent to minimizing connected dominating set in graph theory, and finding a minimum connected dominating set is NP-complete for graphs.
广播过程中最小化参与转发节点数问题与图论中求解最小连通支配集问题等价，而在任意图中求解最小连通支配集是NP完全问题。
Minimizing retransmission nodes in broadcasting is equivalent to minimizing connected dominating set in graph theory, and finding a minimum connected dominating set is NP-complete for graphs.
广播过程中最小化参与转发节点数问题与图论中求解最小连通支配集问题等价，而在任意图中求解最小连通支配集是NP完全问题。
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