First Unique Character in a String LeetCode solution in Java

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class Solution {
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  public int firstUniqChar(String s) {
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    HashMap<Character, Integer> hmap = new HashMap<>();
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    for (int i = 0; i < s.length(); i++) {
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      if (!hmap.containsKey(s.charAt(i))) {
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        hmap.put(s.charAt(i), 1);
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      } else {
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        hmap.put(s.charAt(i), hmap.get(s.charAt(i)) + 1);
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      }
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    }
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    for (int i = 0; i < s.length(); i++) {
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      if (hmap.get(s.charAt(i)) == 1) return i;
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    }
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    return -1;
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  }
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}