text: /*
  393. UTF-8 Validation
  
  A character in UTF8 can be from 1 to 4 bytes long, subjected to the following rules:
  
  For 1-byte character, the first bit is a 0, followed by its unicode code.
  For n-bytes character, the first n-bits are all one's, the n+1 bit is 0, followed by n-1 bytes with most significant 2 bits being 10.
  This is how the UTF-8 encoding would work:
  
     Char. number range  |        UTF-8 octet sequence
        (hexadecimal)    |              (binary)
     --------------------+---------------------------------------------
     0000 0000-0000 007F | 0xxxxxxx
     0000 0080-0000 07FF | 110xxxxx 10xxxxxx
     0000 0800-0000 FFFF | 1110xxxx 10xxxxxx 10xxxxxx
     0001 0000-0010 FFFF | 11110xxx 10xxxxxx 10xxxxxx 10xxxxxx
  Given an array of integers representing the data, return whether it is a valid utf-8 encoding.
  
  Note:
  The input is an array of integers. Only the least significant 8 bits of each integer is used to store the data. 
  This means each integer represents only 1 byte of data.
  
  Example 1:
  
  data = [197, 130, 1], which represents the octet sequence: 11000101 10000010 00000001.
  
  Return true.
  It is a valid utf-8 encoding for a 2-bytes character followed by a 1-byte character.
  Example 2:
  
  data = [235, 140, 4], which represented the octet sequence: 11101011 10001100 00000100.
  
  Return false.
  The first 3 bits are all one's and the 4th bit is 0 means it is a 3-bytes character.
  The next byte is a continuation byte which starts with 10 and that's correct.
  But the second continuation byte does not start with 10, so it is invalid.
  
  */
  
  
  class Solution {
  public:
      bool validUtf8(vector<int>& data) {
          for(int i = 0; i<data.size();){
              int bitsize = leadingbit(data[i]);
              if(bitsize>4 || bitsize == 1) {
                  return false;
              }
              int j = 1;
              while(j<bitsize){ //find the following bit 是否满足条件
                  int bitsize2 = leadingbit(data[j+i]);
                  if(bitsize2!=1) { 
                      return false;
                  }
                  j++;
              }
              i = i + j;
          }
          return true;
      }
      
      int leadingbit(int n){
          int res = 0;
          for(int i = 7; n&(1<<i) && i>=3; i--, res++);
          return res;
      }
  };
  
  /*
  用count判断是不是起点，如果是起点，判断是不是leading bit = 0， 或者有2,3,4个leading bit, 其他情况返回false
  如果有2bit, count = 1;  有3个bit, count = 2;  有四个bit, count = 4;
  
  接下来count>0情况每个数有且仅有一个leading bit, 不满足return false
  
  */
  class Solution {
  public:
      bool validUtf8(vector<int>& data) {
          int count = 0;
          for (const auto& c : data) {
              if (count == 0) {
                  if ((c >> 5) == 0b110) {
                      count = 1;
                  } else if ((c >> 4) == 0b1110) {
                      count = 2;
                  } else if ((c >> 3) == 0b11110) {
                      count = 3;
                  } else if ((c >> 7)) { //开头不是0
                      return false;
                  }
              } else {
                  if ((c >> 6) != 0b10) {
                      return false;
                  }
                  --count;
              }
          }
          return count == 0;
      }
  };