402

class Solution {
public:
    string removeKdigits(string num, int k) {
        int sz = num.size(), rm=0;
        if(sz == k) return "0";
        vector<char> stk;
        for(int i=0; i<sz; i++){
            int curr = num[i];
            while(!stk.empty() && stk.back()>curr && rm<k){
                stk.pop_back();
                rm++;
            }
            if(stk.empty() && curr == '0') continue;
            stk.push_back(curr);
        }
        while(!stk.empty() && rm++ < k) stk.pop_back();
        string ans = string(stk.begin(), stk.end());
        if(ans == "") ans = "0";
        return ans;
    }
};