Google – Run Length Encoding Iterator


Google – Run Length Encoding Iterator
Run length encoding就是比如aaaabbccc压缩成4a2b3c
题目给一个encoding好的string, 比如4a2b3c,要求写一个iterator来遍历原来的string.
[Solution]
除了iterator一般的edge case以外,这道题还需要注意一些其他的edge case,比如0a2b3c,4a0b3c
Idea就是用一个start pointer指向下一个数字,无论下一个是不是0. 如果当前的cnt用完之后,就从start开始往后找下一个不为0的数字。

class EncodingIterator implements Iterator<Character> {
 
  String s;
  int cnt;
  Character c;
  int start;
 
  public EncodingIterator(String s) {
    if (s == null || s.isEmpty()) {
      return;
    }
    this.s = s;
    while (cnt == 0) {
      int i = start;
      for (; i < s.length(); i++) {
        if (!Character.isDigit(s.charAt(i))) {
          break;
        }
      }
      if (i == s.length()) {
        return;
      }
      else {
        this.cnt = Integer.parseInt(s.substring(start, i));
        this.c = s.charAt(i);
        start = i + 1;
      }
    }
  }
 
  @Override
  public boolean hasNext() {
    return c != null;
  }
 
  @Override
  public Character next() {
    if (c == null) {
      return null;
    }
    Character result = c;
    this.cnt--;
    while (cnt == 0) {
      c = null;
      int i = start;
      for (; i < s.length(); i++) {
        if (!Character.isDigit(s.charAt(i))) {
          break;
        }
      }
      if (i == s.length()) {
        break;
      }
      else {
        this.cnt = Integer.parseInt(s.substring(start, i));
        this.c = s.charAt(i);
        start = i + 1;
      }
    }
    return result;
  }
}
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