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by Sumit Chourasia | Oct 03, 2020 | Category :coding | Tags : algorithm data-structure easy leetcode stack

Remove All Adjacent Duplicates In String - Stacks - Easy - LeetCode

Remove All Adjacent Duplicates In String - Stacks - Easy - LeetCode

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

public class Solution {
    public string RemoveDuplicates(string S) {
        var stack = new Stack<char>();
        for(int i=0;i<S.Length;i++){
            if(stack.Count()==0){
                stack.Push(S[i]);
            }
            else{
                if(stack.Peek()==S[i]){
                    stack.Pop();
                }
                else{
                    stack.Push(S[i]);
                }
            }
        }
        
        var sb = new StringBuilder();
        var rev = new Stack<char>();
        while(stack.Count()>0){
            rev.Push(stack.Pop());
        }
        
        while(rev.Count()>0){
            sb.Append(rev.Pop());
        }
        
        return sb.ToString();
    }
}

Time Complexity: O(n)

Space Complexity: O(n)

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