Given two strings S and T, return if they are equal when both are typed into empty text editors. # means a backspace character.

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 = "#a#c"
Output: true
Explanation: Both S and T become "c".

Example 4:

Input: S = "a#c", T = "b"
Output: false
Explanation: S becomes "c" while T becomes "b".

Note:

1. 1 <= S.length <= 200
2. 1 <= T.length <= 200
3. S and T only contain lowercase letters and '#' characters.

想法：使用两个栈，分别处理字符串S和字符串T。对于字符串S而言，逐个遍历该字符串，如果字符不为#,入栈，如果为#，则执行栈的pop()操作。对字符串T也执行同样的操作。最后再比较两个栈中元素是否相等即可

public:
    bool backspaceCompare(string S, string T) {
        std::stack<char> s;
        std::stack<char> t;
        for(char i : S){
            if(i != '#'){
                s.push(i);
            }else if(!s.empty() && i == '#'){
                s.pop();
            }
        }
        for(char j : T){
            if(j != '#'){
                t.push(j);
            }else if(!t.empty() && j == '#'){
                t.pop();
            }
        }
        return s == t;
    }
};