Length of Last Word LeetCode solution in Java

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class Solution {
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  public int lengthOfLastWord(String s) {
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    int j = s.length() - 1, len = 0;
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    boolean flag = true;
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    while (j >= 0 && (flag || (!flag && s.charAt(j) != ' ')))
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      if (s.charAt(j--) != ' ') {
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        flag = false;
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        len++;
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      }
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    return len;
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  }
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}