feat: add solutions to lc problem: No.393

[yanglbme]

No.0393.UTF-8 Validation

[thinkasany]

其实有点魔法字符串了
copilot 是这样子建议的，不过处于做题的话，那样子应该问题也不大，但是 js还是都用上 === 三等吧

function isSingleByte(v: number): boolean {
  return (v >> 7) === 0;
}

function isContinuationByte(v: number): boolean {
  return (v >> 6) === 0b10;
}

function getContinuationBytesCount(v: number): number {
  if ((v >> 5) === 0b110) return 1;
  if ((v >> 4) === 0b1110) return 2;
  if ((v >> 3) === 0b11110) return 3;
  return -1;
}

function validUtf8(data: number[]): boolean {
  let cnt = 0;
  for (const v of data) {
    if (cnt > 0) {
      if (!isContinuationByte(v)) {
        return false;
      }
      --cnt;
    } else if (isSingleByte(v)) {
      cnt = 0;
    } else {
      const newCnt = getContinuationBytesCount(v);
      if (newCnt === -1) {
        return false;
      }
      cnt = newCnt;
    }
  }
  return cnt === 0;
}