Backspace String Compare

 Given two strings s and t, return true if they are equal when both are typed into empty text editors. '#' means a backspace character.


Note that after backspacing an empty text, the text will continue empty.


 


Example 1:


Input: s = "ab#c", t = "ad#c"

Output: true

Explanation: Both s and t become "ac".

Example 2:


Input: s = "ab##", t = "c#d#"

Output: true

Explanation: Both s and t become "".

Example 3:


Input: s = "a#c", t = "b"

Output: false

Explanation: s becomes "c" while t becomes "b".

 


Constraints:


1 <= s.length, t.length <= 200

s and t only contain lowercase letters and '#' characters.

 


Follow up: Can you solve it in O(n) time and O(1) space?



class Solution {
    public boolean backspaceCompare(String s, String t) {
   
    return build(s).equals(build(t));
    }
    public static  String build(String str)
    {
        Stack<Character> st= new Stack<>();

        for(char c :str.toCharArray())
        {

            if(c !='#')
            {
                st.push(c);
            }
            else if(!st.isEmpty())
            {
                st.pop();
            }
        }
        StringBuilder result=new StringBuilder();
        for(char c :st)
        {
            result.append(c);
        }
        return result.toString();
    }
}

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