Remove K Digits

class Solution {
public:
    string removeKdigits(string num, int k) {
        string st;
        for (char c : num) {
            while (!st.empty() && st.back() > c && k > 0) {
                st.pop_back(); --k;
            }
            st.push_back(c);
        }
        while (k-- > 0 && !st.empty()) st.pop_back();
        int start = 0;
        while (start < (int)st.size() && st[start] == '0') ++start;
        string ans = st.substr(start);
        return ans.empty() ? "0" : ans;
    }
};

func removeKdigits(num string, k int) string {
    st := []byte{}
    for i := 0; i < len(num); i++ {
        c := num[i]
        for len(st) > 0 && st[len(st)-1] > c && k > 0 {
            st = st[:len(st)-1]
            k--
        }
        st = append(st, c)
    }
    for k > 0 && len(st) > 0 {
        st = st[:len(st)-1]
        k--
    }
    start := 0
    for start < len(st) && st[start] == '0' {
        start++
    }
    ans := string(st[start:])
    if ans == "" {
        return "0"
    }
    return ans
}

class Solution:
    def removeKdigits(self, num: str, k: int) -> str:
        st: list[str] = []
        for c in num:
            while st and st[-1] > c and k > 0:
                st.pop()
                k -= 1
            st.append(c)
        while k > 0 and st:
            st.pop()
            k -= 1
        start = 0
        while start < len(st) and st[start] == '0':
            start += 1
        ans = ''.join(st[start:])
        return ans if ans else "0"

function removeKdigits(num, k) {
    const st = [];
    for (const c of num) {
        while (st.length && st[st.length - 1] > c && k > 0) {
            st.pop();
            k--;
        }
        st.push(c);
    }
    while (k > 0 && st.length) {
        st.pop();
        k--;
    }
    let start = 0;
    while (start < st.length && st[start] === '0') start++;
    const ans = st.slice(start).join('');
    return ans === '' ? '0' : ans;
}

class Solution {
    public String removeKdigits(String num, int k) {
        StringBuilder st = new StringBuilder();
        for (int i = 0; i < num.length(); i++) {
            char c = num.charAt(i);
            while (st.length() > 0 && st.charAt(st.length() - 1) > c && k > 0) {
                st.deleteCharAt(st.length() - 1);
                k--;
            }
            st.append(c);
        }
        while (k > 0 && st.length() > 0) {
            st.deleteCharAt(st.length() - 1);
            k--;
        }
        int start = 0;
        while (start < st.length() && st.charAt(start) == '0') start++;
        String ans = st.substring(start);
        return ans.isEmpty() ? "0" : ans;
    }
}

function removeKdigits(num: string, k: number): string {
    const st: string[] = [];
    for (const c of num) {
        while (st.length && st[st.length - 1] > c && k > 0) {
            st.pop();
            k--;
        }
        st.push(c);
    }
    while (k > 0 && st.length) {
        st.pop();
        k--;
    }
    let start = 0;
    while (start < st.length && st[start] === '0') start++;
    const ans = st.slice(start).join('');
    return ans === '' ? '0' : ans;
}