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Given a non-negative integer S represented as a string, remove K digits from the number so that the new number is the smallest possible.

**Note : **The given *num* does not contain any leading zero.

**Example 1:**

**Input:**
S = "149811", K = 3
**Output:** 111
**Explanation**: Remove the three digits
4, 9, and 8 to form the new number 111
which is smallest.

**Example 2:**

**Input**:
S = "1002991", K = 3
**Output:** 21
**Explanation**: Remove the three digits 1(leading
one), 9, and 9 to form the new number 21(Note
that the output must not contain leading
zeroes) which is the smallest.

**Your Task:**

You don't need to read input or print anything. Your task is to complete the function **removeKdigits() **which takes the string S and an integer K as input and returns the new number which is the smallest possible.

**Expected Time Complexity: **O(|S|).

**Expected Auxiliary Space: **O(|S|).

**Constraints:**

1<=|S|<=10002

1<=K<=|S|

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Remove K Digits

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