remove k digits 2

//https://leetcode.com/problems/remove-k-digits/description/

#include <iostream>

using namespace std;

class Solution {
private:
    inline void AddDigit(string &ret, char c, bool &leadingZeroes) {
        if (!leadingZeroes || c != '0') {
            ret += c;
            leadingZeroes = false;
        }
    }

public:
    string removeKdigits(string nums, int k) {
        if (nums.size() == k)
            return "0";

        string ret = "";
        char lastCh = '#';
        bool leadingZeroes = true;

        //remove all digits greater then the following one while k > 0
        for (char c : nums) {
            if (lastCh == '#') {
                lastCh = c;
                continue;
            }

            if (lastCh <= c) {
                AddDigit(ret, lastCh, leadingZeroes);
                lastCh = c;
            }
            else {
                if (k > 0)
                    k--;
                else
                    AddDigit(ret, lastCh, leadingZeroes);
                lastCh = c;
            }
        }
        AddDigit(ret, lastCh, leadingZeroes);

        //trim digits from the end, skip zeroes
        if (k > 0)
            for (long i = ret.size() - 1; i >= 0; i--) {
                if (ret[i] != '0') {
                    ret.erase(i, 1);
                    k--;
                }
                if (k == 0)
                    break;
            }

        if (ret == "")
            ret = "0";

        return ret;
    }
};