Approach: Stack

def removeStars(s):
    st = []
    for c in s:
        if c == "*": st.pop()
        else: st.append(c)
    return "".join(st)

Complexity: O(n) time, O(n) space.

Full Solution — all languages

class Solution:
    def removeStars(self, s):
        st = []
        for c in s:
            if c == "*":
                st.pop()
            else:
                st.append(c)
        return "".join(st)

import java.util.*;
class Solution {
    public String removeStars(String s) {
        StringBuilder sb = new StringBuilder();
        for (char c : s.toCharArray()) {
            if (c == '*') sb.deleteCharAt(sb.length() - 1);
            else sb.append(c);
        }
        return sb.toString();
    }
}

#include <bits/stdc++.h> using namespace std;
class Solution {
    public: string removeStars(string s) {
        string st;
        for (char c : s) {
            if (c == '*') st.pop_back();
            else st.push_back(c);
        }
        return st;
    }
};

/**
 * @param {string} s
 * @return {string}
 */ var removeStars = function(s) {
    const st = [];
    for (const c of s) {
        if (c === '*') st.pop();
        else st.push(c);
    }
    return st.join('');
};

Removing Stars From a String

Example 1

Example 2

Constraints