1047_Remove_adjacent_duplicates

// https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string/

// My solution

class Solution {
    public String removeDuplicates(String S) {
        Stack<Character> stack = new Stack<Character>();
        char[] arr = S.toCharArray();
        for (char ch : arr) {
            if (!stack.isEmpty() && stack.peek() == ch) {
                stack.pop();
            }
            else {
                stack.push(ch);
            }
        }
        StringBuilder sb = new StringBuilder();
        while (!stack.isEmpty()) {
            sb.append(stack.pop());
        }
        sb.reverse();
        return sb.toString();
    }
}

// Other solution

public String removeDuplicates(String s) {
        int i = 0, n = s.length();
        char[] res = s.toCharArray();
        for (int j = 0; j < n; ++j, ++i) {
            res[i] = res[j];
            if (i > 0 && res[i - 1] == res[i]) // count = 2
                i -= 2;
        }
        return new String(res, 0, i);
    }