Remove All Adjacent Duplicates in String II

Description

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"
Explanation: 
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"

 

Constraints:

• 1 <= s.length <= 10^5
• 2 <= k <= 10^4
• s only contains lower case English letters.

Solution(javascript)

/*
 * @lc app=leetcode id=1209 lang=javascript
 *
 * [1209] Remove All Adjacent Duplicates in String II
 */

// @lc code=start
/**
 * @param {string} s
 * @param {number} k
 * @return {string}
 */
const removeDuplicates = function (s, k) {
  const stack = []
  for (const c of s) {
    if (stack.length && c === stack[stack.length - 1][0]) {
      stack[stack.length - 1] += c
      if (stack[stack.length - 1].length === k) {
        stack.pop()
      }
    } else {
      stack.push(c)
    }
  }
  return stack.join('')
}