1
class Solution {
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  public boolean validUtf8(int[] data) {
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    return help(data, 0);
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  }
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  public boolean help(int[] data, int index) {
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    int n = data.length - index;
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    if (n == 0) {
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      return true;
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    }
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    int c0 = count(data[index]);
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    if (c0 < 0 || c0 > n) {
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      return false;
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    }
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    for (int i = index + 1; i < index + c0; i++) {
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      if ((data[i] & 0b10000000) != 0b10000000) {
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        return false;
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      }
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    }
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    return help(data, index + c0);
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  }
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  private int count(int a) {
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    if ((a >> 3) == 0b11110) {
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      return 4;
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    } else if ((a >> 4) == 0b1110) {
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      return 3;
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    } else if ((a >> 5) == 0b110) {
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      return 2;
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    } else if ((a >> 7) == 0) {
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      return 1;
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    }
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    return -1;
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  }
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}