java有 1、2、3、4四个数字能组成多少个互不相同且无重复数字的三位数？都是多少？

Java has 4 digits: 1, 2, 3, and 4. We need to find out how many unique three-digit numbers can be formed using these digits.

To solve this problem, we can use the concept of permutations. The number of permutations of n objects taken r at a time is given by the formula:

P(n, r) = n! / (n - r)!

In this case, we want to find the number of permutations of 4 digits taken 3 at a time: P(4, 3) = 4! / (4 - 3)! = 4! / 1! = 4 * 3 * 2 = 24.

Therefore, we can form a total of 24 unique three-digit numbers using the digits 1, 2, 3, and 4. The numbers are:

123, 124, 132, 134, 142, 143, 213, 214, 231, 234, 241, 243, 312, 314, 321, 324, 341, 342, 412, 413, 421, 423, 431, 432