YouTube Software Programmer interview questions

The first interview asks about the change combination problem. First it was able to be solved by greedy alg but then the condition changed and turn into a DP problem. The second interview asks to substitute *s in a string by binary numbers. For example, input aa*bbb*c, the output should be four strings: aa0bbb0c, aa0bbb1c, aa1bbb0c, aa1bbb1c