Count Number of Special Subsequences LeetCode solution in Java

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class Solution {
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  public int countSpecialSubsequences(int[] nums) {
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    long z = 0; // starting and ending with zero
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    long zo = 0; // starting with zero and ending with One
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    long zot = 0; // starting with zero and ending Two
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    int mod = 1000000007;
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    for (int i : nums) {
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      if (i == 0) {
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        z = ((2 * z) % mod + 1) % mod; // zero = 2*zero+1
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      } else if (i == 1) {
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        zo = ((2 * zo) % mod + z % mod) % mod; // zero = 2*zeroOne+zero
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      } else {
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        zot = ((2 * zot) % mod + zo % mod) % mod; // zeroOneTwo = 2*zeroOneTwo+zeroOne
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      }
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    }
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    return (int) (zot % mod);
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  }
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}