Problem 26: Remove K digits to create smallest number[Microsoft]

String Manipulation, Integer Typecasting, Greedy Approach

Problem

This problem was asked by Microsoft.

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

Example 1

Input: num = "1432219", k = 3
Output: "1219"
Explanation: Remove the three digits 4, 3, and 2 to form the new number 1219 which is the smallest.

Example 2

Input: num = "10200", k = 1
Output: "200"
Explanation: Remove the leading 1 and the number is 200. Note that the output must not contain leading zeroes.

Example 3

Input: num = "10", k = 2
Output: "0"
Explanation: Remove all the digits from the number and it is left with nothing which is 0.

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