LeetCode 1047. Remove All Adjacent Duplicates In String

原题链接在这里：https://leetcode.com/problems/remove-all-adjacent-duplicates-in-string/

题目：

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:

Note:

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

题解：

Follow the instructions, and remove 2 consecutive same chars.

Time Complexity: O(n^2). n = S.length().

Space: O(n).

AC Java:

 1 class Solution {
 2     public String removeDuplicates(String S) {
 3         if(S == null || S.length() == 0){
 4             return S;
 5         }
 6         
 7         boolean changed = true;
 8         while(changed){
 9             changed = false;
10             StringBuilder sb = new StringBuilder();
11             int i = 0;
12             while(i < S.length()){
13                 if(i == S.length() - 1 || S.charAt(i) != S.charAt(i + 1)){
14                     sb.append(S.charAt(i));
15                     i++;
16                 }else{
17                     changed = true;
18                     int j = i + 1;
19                     int count = 1;
20                     while(j < S.length() && S.charAt(i) == S.charAt(j) && count < 2){
21                         j++;
22                         count++;
23                     }
24                     
25                     i = j;
26                 }
27             }
28             
29             S = sb.toString();
30         }
31         
32         return S;
33     }
34 }

跟上Remove All Adjacent Duplicates in String II.