string is composed ofn(20) characters in an orderly sequence recorded as s:“c1C2C3…Cn” S is string name c123n is value is a character n is string length Such as,S=“ TSinghua University
1 Graphs and Trees The following two definitions of a tree are equivalent Definition 1: A tree is an acyclic graph of n vertices that has n-1 edges Definition 2: A tree is a connected graph such that Vu, v E V, there is a unique path connecting u to u. In general, when we want to show the equivalence of two definitions, we must show