说明：  回朔法的讨论，鸽笼原理，Ramsey问题。排列组合问题，容斥原理，母函数，递归关系，线性规划，动态规划。Polya原理
(Discussion back method, the pigeonhole principle, Ramsey problems. Permutations and combinations, the principle of inclusion and exclusion, generating functions, recursion relations, linear programming, dynamic programming. Polya principle)