Formatted question description: https://leetcode.ca/all/1047.html

1047. Remove All Adjacent Duplicates In String (Easy)

Given a string S of lowercase letters, a duplicate removal consists of choosing two adjacent and equal letters, and removing them.

We repeatedly make duplicate removals on S until we no longer can.

Return the final string after all such duplicate removals have been made.  It is guaranteed the answer is unique.

 

Example 1:

Input: "abbaca"
Output: "ca"
Explanation: 
For example, in "abbaca" we could remove "bb" since the letters are adjacent and equal, and this is the only possible move.  The result of this move is that the string is "aaca", of which only "aa" is possible, so the final string is "ca".

 

Note:

  1. 1 <= S.length <= 20000
  2. S consists only of English lowercase letters.

Related Topics:
Stack

Similar Questions:

Solution 1.

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

// Time: O(N)
// Space: O(1)
class Solution {
public:
    string removeDuplicates(string s) {
        string ans;
        for (char c : s) {
            if (ans.empty() || c != ans.back()) ans += c;
            else ans.pop_back();
        }
        return ans;
    }
};

Java

class Solution {
    public String removeDuplicates(String S) {
        Stack<Character> stack = new Stack<Character>();
        int length = S.length();
        for (int i = length - 1; i >= 0; i--) {
            char c = S.charAt(i);
            if (stack.isEmpty() || stack.peek() != c)
                stack.push(c);
            else
                stack.pop();
        }
        StringBuffer sb = new StringBuffer();
        while (!stack.isEmpty())
            sb.append(stack.pop());
        return sb.toString();
    }
}

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