Number of Ways to Split a String LeetCode solution in Java

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class Solution {
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  public int numWays(String s) {
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    long n = s.length();
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    long one = 0; // to count number of ones
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    long mod = 1_000_000_007;
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    char[] c = s.toCharArray();
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    for (int i = 0; i < c.length; i++) {
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      if (c[i] == '1') one++;
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    }
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    // there will be 3 cases
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    // 1.no ones present in the string
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    // 2.number of ones present in the string isnt divisible by 3(since we need to cut 3 parts)
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    // 3.number of ones divisible by 3
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    if (one == 0) // case 1
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    {
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      return (int) ((((n - 1) * (n - 2)) / 2) % mod);
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    }
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    if (one % 3 != 0) // case 2,which means we cant split ones equally
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    return 0;
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    // case 3
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    long ones = one / 3; // number of ones that should be present in each part
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    one = 0;
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    long part1 = 0; // number of ways in which part1 and part2 can be split
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    long part2 = 0;
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    for (int i = 0; i < c.length; i++) {
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      if (c[i] == '1') one++;
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      if (one == ones) part1++;
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      if (one == 2 * ones) part2++;
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    }
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    return (int) ((part1 * part2) % mod);
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  }
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}