# LeetCode Remove K Digits

LeetCode Remove K Digits

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.```

```class Solution {
public:
string removeKdigits(string num, int k) {
if (k >= num.size())return "0";
string ans = "";
for (const auto& c : num) {
if (ans.empty() || k == 0)ans.push_back(c);
else {
while (!ans.empty() && ans.back() > c) {
ans.pop_back();
if (--k == 0)break;
}
ans.push_back(c);
}
}
while (k-- > 0 && !ans.empty()) ans.pop_back();
while (!ans.empty() && ans[0] == '0')ans.erase(ans.begin());
return ans.empty() ? "0" : ans;
}
};
```