# Remove K Digits

#1

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.

Note:

• The length of num is less than 10002 and will be ≥ k.
• The given num does not contain any leading zero.

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.
```

#2

The below code uses a stack to remove `k` elements from the given string.

``````class Solution {
public String removeKdigits(String num, int k) {
if(k==num.length()) return "0";
Stack<Character> stack = new Stack<>();
int i=0;
while(i<num.length()){
while(k>0 && !stack.isEmpty() && stack.peek() > num.charAt(i)){
stack.pop();
k--;
}
stack.push(num.charAt(i));
i++;
}

while(k>0){
stack.pop();
k--;
}

StringBuilder result = new StringBuilder();
while(!stack.isEmpty()){
result.append(stack.pop());
}
result.reverse();

//remove all the 0 at the head
while(result.length()>1 && result.charAt(0)=='0')
result.deleteCharAt(0);

return result.toString();

}
}
``````