java 删除重复字母 - 去重字符 - 难

Posted 2021-05-07

public String removeDup(String s){
  if(s==null || s.length()==0) return "";
  int[] carry = new int[26];
  for(char c : s) carry[c-'a']++;
  Set<Character> s = new HashSet<>(); //保存unique字符
  Stack<Character> stack = new Stack<>(); //这就是单调栈，但不是严格的单调栈
  for(int i = 0 ; i < s.length(); i++){
    if(!s.contains(s.charAt(i))){
      while(!stack.isEmpty() && stack.peek()>s.charAt(i) && carry[stack.peek()-'a']>0){
        s.remove(stack.peek());
        stack.pop();
      }
      stack.push(s.charAt(i));
      s.add(s.charAt(i));
    }
    carry[s.charAt(i)-'a']--;
  }
  return stack.toString();
}
//牛逼