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class Solution {
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  public String validIPAddress(String IP) {
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    if (IP.length() == 0) return "Neither";
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    if (IP.indexOf(".") >= 0) return validateIPV4(IP);
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    if (IP.indexOf(":") >= 0) return validateIPV6(IP);
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    return "Neither";
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  }
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  private String validateIPV4(String ip) {
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    // step 1
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    if (ip.charAt(0) == '.' || ip.charAt(ip.length() - 1) == '.') return "Neither";
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    // step 2
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    String[] component = ip.split("\\.");
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    // step 3
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    if (component.length != 4) return "Neither";
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    // step 4
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    for (String comp : component) {
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      if (comp.length() == 0 || comp.length() > 3 || (comp.charAt(0) == '0' && comp.length() > 1)) {
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        return "Neither";
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      }
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      // step5
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      for (char ch : comp.toCharArray()) {
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        if (ch < '0' || ch > '9') return "Neither";
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      }
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      // step6
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      int num = Integer.parseInt(comp);
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      if (num < 0 || num > 255) return "Neither";
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    }
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    return "IPv4";
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  }
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  private String validateIPV6(String ip) {
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    if (ip.charAt(0) == ':' || ip.charAt(ip.length() - 1) == ':') return "Neither";
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    String[] component = ip.split(":");
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    if (component.length != 8) return "Neither";
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    for (String comp : component) {
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      if (comp.length() == 0 || comp.length() > 4) return "Neither";
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      for (char ch : comp.toLowerCase().toCharArray()) {
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        if ((ch < '0' || ch > '9')
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            && (ch != 'a' && ch != 'b' && ch != 'c' && ch != 'd' && ch != 'e' && ch != 'f')) {
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          return "Neither";
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        }
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      }
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    }
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    return "IPv6";
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  }
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}