DFS + Cycles + Cactus
We found a dictionary of the Ancient Civilization Mayo (ACM) during excavation of the ruins. After analysis of the dictionary, we revealed they used a language that had not more than 26 letters. So one of us mapped each letter to a different English alphabet and typed all the words in the dictionary into a computer.
How the words are ordered in the dictionary, especially whether they are ordered lexicographically, is an interesting topic to many people. As a good programmer, you are requested to write a program to judge whether we can consider the words to be sorted in a lexicographical order.
Note: In a lexicographical order, a word always precedes other words it is a prefix of. For example, "ab" precedes "abc", "abde", and so on.
Consists of multiple datasets. Each dataset is formatted as follows:
. . .
Each dataset consists of n + 1 lines. The first line of each dataset contains an integer that indicates n (1 ≤ n ≤ 500). The i-th line of the following n lines contains string[i], which consists of up to 10 English lowercase letters.
The end of the input is "0", and this should not be processed.
Print either "yes" or "no" in a line for each dataset, in the order of the input. If all words in the dataset can be considered to be ordered lexicographically, print "yes". Otherwise, print "no".
4 cba cab b a 3 bca ab a 5 abc acb b c c 5 abc acb c b b 0
yes no yes no