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Remove All Adjacent Duplicates in String II

Updated: Apr 16, 2021

Given a string s, a k duplicate removal consists of choosing k adjacent and equal letters from s and removing them causing the left and the right side of the deleted substring to concatenate together.

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

Return the final string after all such duplicate removals have been made.

It is guaranteed that the answer is unique.

Example 1:

Input: s = "abcd", k = 2
Output: "abcd"
Explanation: There's nothing to delete.

Example 2:

Input: s = "deeedbbcccbdaa", k = 3
Output: "aa"
First delete "eee" and "ccc", get "ddbbbdaa"
Then delete "bbb", get "dddaa"
Finally delete "ddd", get "aa"

Example 3:

Input: s = "pbbcggttciiippooaais", k = 2
Output: "ps"


  • 1 <= s.length <= 10^5

  • 2 <= k <= 10^4

  • s only contains lower case English letters.


class Solution {
    public String removeDuplicates(String s, int k) {
        int count=1;
        for(int i=1;i<s.length();i++)
            if(s.charAt(i)==s.charAt(i-1)) count=count+1;
            else count=1;
            if(count==k) s=removeDuplicates(s.substring(0,i-k+1)+s.substring(i+1),k);
         return s; 

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