我有一个像0189，为此，我需要生成所有的子序列的字符串，但单个字符的顺序必须保持，也就是说，这里9不应该来之前0,1或8例：0， 018，01，09，0189，18，19，019，等等。

I have a string like "0189", for which I need to generate all subsequences, but the ordering of the individual characters must be kept, i.e, here 9 should not come before 0, 1 or 8. Ex: 0, 018, 01, 09, 0189, 18, 19, 019, etc.

另一个例子是10292，这个子序列是：1，10，02，02，09，29，92，等等。正如你可能已经注意到02两次，因为2在谈到两次给定的字符串。但同样的事情，如：21，01，91是无效的，因为为了要维持

Another example is "10292" for which subsequences would be: 1, 10, 02, 02, 09, 29, 92, etc. As you might have noticed '02' two times, since '2' comes twice in the given string. But again things like: 21, 01, 91 are invalid as order is to be maintained.

任何算法或伪code，它可以在C / C实现++将AP preciated！

Any algorithm or psuedo code, which could be implemented in C/C++ would be appreciated!

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