Problem
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 <= S.length <= 200
1 <= 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?
Solution
class Solution {
public boolean backspaceCompare(String S, String T) {
return helper(S).equals(helper(T));
}
private String helper(String str) {
int count = 0;
String res = "";
for (int i = str.length()-1; i >= 0; i--) {
char ch = str.charAt(i);
if (ch == `#`) count++;
else {
if (count > 0) count--; //能不加就不加
else res += ch; //非加不可的字元 那就加吧
}
}
return res;
}
}