Number of Unique Good Subsequences LeetCode solution in Java

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class Solution {
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  public int numberOfUniqueGoodSubsequences(String binary) {
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    int initialZeroCount = 0;
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    while (initialZeroCount < binary.length() && binary.charAt(initialZeroCount) == '0')
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      initialZeroCount++;
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    if (initialZeroCount == binary.length()) return 1;
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    long[] dp = new long[binary.length()];
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    dp[initialZeroCount] = 1;
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    int lastOne = 0, lastZero = 0;
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    long mod = (long) Math.pow(10, 9) + 7;
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    for (int i = initialZeroCount + 1; i < binary.length(); i++) {
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      int j = binary.charAt(i) == '1' ? lastOne : lastZero;
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      long dup = j > 0 ? dp[j - 1] : 0;
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      dp[i] = 2 * dp[i - 1] - dup;
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      if (dp[i] < 0) dp[i] += mod;
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      dp[i] %= mod;
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      if (binary.charAt(i) == '0') lastZero = i;
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      else lastOne = i;
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    }
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    int hasZero = 0;
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    if (binary.contains("0")) hasZero = 1;
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    return (int) (dp[binary.length() - 1] + hasZero);
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  }
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}