Find Longest Awesome Substring LeetCode solution in Java

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class Solution {
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  public int longestAwesome(String s) {
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    Map<Integer, Integer> map = new HashMap<>();
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    map.put(0, -1);
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    int state = 0;
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    int ans = 0;
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    for (int i = 0; i < s.length(); i++) {
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      int bit = (1 << (s.charAt(i) - '0'));
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      state ^= bit; // if odd freq then it becomes even or if even becomes odd
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      if (map.containsKey(state)) ans = Math.max(ans, i - map.get(state));
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      for (int odd = 0; odd <= 9; odd++) { // become odds one by one
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        int mask = (1 << odd);
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        Integer j = map.get(state ^ mask);
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        if (j != null) ans = Math.max(ans, i - j);
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      }
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      if (!map.containsKey(state)) map.put(state, i);
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    }
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    return ans;
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  }
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}