Example 1: From 10 English letters $A, B, C, D, E$, $F, G, X, Y, Z$, select 5 letters (letters can be repeated) to form a word. Arrange all possible words in "dictionary order" (i.e., the order in which English words are arranged in an English-Chinese dictionary), resulting in a word list $A 1 A A A A, A A A A E, A A A A C$, $\cdots, ~ A A A A Z, \triangle A A B A, \triangle A A B B, \cdots, D E-$ $G X Y, D E G X Z, D E G Y A, \cdots, \quad Z Z Z Z Y$, $Z Z Z Z Z$. Let the number of words between $C Y Z G B$ and $X E F D A$ (excluding these two words) be $k$. Write down the $k$-th word in the word list.
(1988, Jiangsu Province High School Mathematics Competition)
Analysis: 10 letters, allowing repetition, are used to form 5-letter words, resulting in a total of 100,000 possible words. Solving this problem directly through permutations would be extremely difficult. However, if we assign values to the letters $A, B, \cdots, Y, Z$, the problem can be transformed into a numerical problem.

Solution: Assign the values $0,1,2, \cdots, 9$ to the letters $A, B, C, D, E, F, G, X, Y, Z$ respectively. This way, the "ordered" arrangement of words becomes the numbers $0,1,2, \cdots, 99999$. Thus, the words CYZGB and XEFDA are transformed into the numbers 28961 and 74530, respectively. Therefore, $k=74530-28961-1=45568$. Noting that $A A A A A$ becomes 0, the $k$-th word corresponds to the number 45567, which is EFFGX.

The assignment method is a specific form of the transformation idea in problem-solving. From the above example, we can see that the thinking pattern of the assignment method is:

Through the above example, we can also see that the advantage of the assignment method lies in: By assigning values, it transforms complex problems into simpler ones, and at the same time, it can convert abstract mathematical reasoning into concrete mathematical operations.

The assignment method can be applied in problem-solving in the following aspects:  
By assigning special values to the elements in the problem, it transforms the problem into a numerical problem, thus creating conditions for solving the problem through arithmetic or algebraic operations.