Clear Digits

There have been quite the number of Easy questions this month.

Since we only delete the first digit and the closest non-digit character to its left, you could just iterate through s in reverse and just not append the letters after a digit character to ans. (of course, you still have to flip the string)

code

class Solution {
public:
    string clearDigits(string s) {
        string ans = "";
        int counter = 0;
        for (int i = s.size()-1; i >= 0; --i) {
            if (s[i]-'0' >= 0 && s[i]-'0' <= 9) {
                ++counter;
            } else if (counter > 0) {
                --counter;
            } else {
                ans += s[i];
            }
        }
        reverse(ans.begin(), ans.end());
        return
    }
};

complexity

• Time: O(n)
• Space: O(n)