CodeForces 102C Homework​求助

输入描述:

			
			

				The first input data line contains a string whose length is equal to n (1 ≤ n ≤ 105). The string consists of lowercase Latin letters. The second line contains the number k (0 ≤ k ≤ 105).
			

输出描述:

			
			

				Print on the first line the only number m — the least possible number of different characters that could remain in the given string after it loses no more than k characters.
			

			

				Print on the second line the string that Gerald can get after some characters are lost. The string should have exactly m distinct characters. The final string should be the subsequence of the initial string. If Gerald can get several different strings with exactly m distinct characters, print any of them.
			

aaaaa
4
abacaba
4
abcdefgh
10

1
aaaaa
1
aaaa
0

备注:

			
			

				In the first sample the string consists of five identical letters but you are only allowed to delete 4 of them so that there was at least one letter left. Thus, the right answer is 1 and any string consisting of characters "a" from 1 to 5 in length.
			

			

				In the second sample you are allowed to delete 4 characters. You cannot delete all the characters, because the string has length equal to 7. However, you can delete all characters apart from "a" (as they are no more than four), which will result in the "aaaa" string.
			

			

				In the third sample you are given a line whose length is equal to 8, and k = 10, so that the whole line can be deleted. The correct answer is 0 and an empty string.