Number of Ways to Split a String LeetCode solution in C++

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class Solution {
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 public:
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  int MOD = 1e9 + 7;
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  int numWays(string s) {
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    int ones = count(begin(s), end(s), '1'), n = s.size();
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    if (ones % 3) return 0;
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    if (!ones) return (((n - 1) * 1LL * (n - 2) * 1LL) / 2) % MOD; /// n- 1 C 2
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    int left = 0, right = 0, count = 0, i = 0;
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    while (count <= ones / 3) {
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      count += s[i++] == '1';
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      if (count == ones / 3) ++left;
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    }
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    i = n - 1, count = 0;
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    while (count <= ones / 3) {
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      count += s[i--] == '1';
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      if (count == ones / 3) ++right;
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    }
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    return (left * 1LL * right * 1LL) % MOD;
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  }
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};