Day 13 Remove K Digits.cpp

PROBLEM:


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.



SOLUTION:



class Solution {
public:
    string removeKdigits(string num, int k) {
        
        int i;
        string s;
        
        if(k==0)
            return num;
        
        if(k>=num.length())
        {
            s="0";
            return s;
        }
        
        for (const auto c : num) {
            while (k > 0 && !s.empty() && s.back() > c) {
                s.pop_back();
                k--;
            }
            s.push_back(c);
        }

        
        s.resize(s.length() - k);
        
        for(i=0;i<s.length();i++)
        {
            if(s[i]!='0')
            {
                break;
            }
        }
        
        s=s.substr(i,s.length()-i);
        
        if(s.empty())
            s="0";
        
        return s;
    }
};