1209. Remove All Adjacent Duplicates in String II

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"
分析：
我们把每个letter对应的出现次数放在stack里面，当==k的时候，就pop.

class Solution {
    public String removeDuplicates(String s, int k) {
        int len = s.length();
        Stack<Node> stack = new Stack<>();
        for (char c : s.toCharArray()) {
            if (!stack.isEmpty() && stack.peek().c == c) {
                stack.peek().count++;
            } else {
                stack.push(new Node(c, 1));
            }
            if (stack.peek().count == k)
                stack.pop();
        }
        // build result
        StringBuilder sb = new StringBuilder();
        for (Node node : stack) {
            for (int i = 0; i < node.count; i++) {
                sb.append(node.c);
            }
        }
        return sb.toString();
    }
}

class Node {
    char c;
    int count;

    public Node(char c, int count) {
        this.c = c;
        this.count = count;
    }
}