Leetcode•Aug 07, 2025
Backspace String Compare
Hazrat Ali
Leetcode
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".
Solution
/**
* @param {string} S
* @param {string} T
* @return {boolean}
*/
const backspaceCompare = (S, T) => {
for (let i = S.length - 1, j = T.length - 1, skipS = 0, skipT = 0; i >= 0 || j >= 0; i--, j--) {
while (i >= 0) {
if (S[i] === '#') {
skipS++;
i--;
} else if (skipS > 0) {
skipS--;
i--;
} else break;
}
while (j >= 0) {
if (T[j] === '#') {
skipT++;
j--;
} else if (skipT > 0) {
skipT--;
j--;
} else break;
}
if (i >= 0 && j >= 0 && S[i] != T[j]) {
return false;
}
if (i >= 0 !== j >= 0) {
return false;
}
}
return true;
};