LeetCode: Remove All Adjacent Duplicates in String II

Remove All Adjacent Duplicates in String II

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• Tag: #stack

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.

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.

• Solution:

// https://code.dennyzhang.com/remove-all-adjacent-duplicates-in-string-ii
// Basic Ideas: stack
//
// Complexity: Time O(n), Space O(n)
type MyNode struct {
    ch byte
    cnt int
}

func removeDuplicates(s string, k int) string {
    stack := []MyNode{}
    for i, _ := range s {
        ch := s[i]
        if len(stack)>0 && stack[len(stack)-1].ch == ch {
            stack[len(stack)-1].cnt += 1
            if stack[len(stack)-1].cnt == k {
                stack = stack[0:len(stack)-1]
            }
        } else {
            stack = append(stack, MyNode{ch:ch, cnt:1})
        }
    }
    l := []byte{}
    for _, node := range stack {
        for i:=0; i<node.cnt; i++ {
            l = append(l, node.ch)
        }
    }
    return string(l)
}