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Problem solution · Java

Validate IP Address

Validate IP Address: a Java solution using direct simulation. Learn the idea, check the complexity, and read the full code, with credit to walkccc LeetCode Solutions.

Technique
Direct simulation
Source
walkccc LeetCode Solutions
Length
47 lines
Start with the idea.

Try the problem first. If you get stuck, read the approach below, then write your own solution. The full code is at the bottom.

Approach

Direct simulation

For Validate IP Address, the implementation follows the problem’s operations directly while maintaining only the state needed for the next decision.

  1. Translate each rule into one explicit state update.
  2. Maintain the invariant after every processed item.
  3. Return the accumulated state once all relevant input has been handled.

Code notes

  • 47 lines of Java from the credited upstream file 468.java.
  • The implementation keeps its working state in language-native values and containers.
  • 4 loop blocks detected.

Complexity

Count the number and nesting of passes over the input, then include the maintained containers in the memory estimate.

Check the problem constraints before deciding whether this complexity will pass.

Source

Code and credit

This code comes from walkccc LeetCode Solutions by P.-Y. Chen (walkccc) and is used under the MIT licence.

Open problem ↗Original source ↗
Full codeValidate IP Address · JavaJava
Use this to learn the idea, then write your own version.
class Solution {  public String validIPAddress(String queryIP) {    if (queryIP.chars().filter(c -> c == '.').count() == 3) {      for (final String digit : queryIP.split("\\.", -1))        if (!isIPv4(digit))          return "Neither";      return "IPv4";    }     if (queryIP.chars().filter(c -> c == ':').count() == 7) {      for (final String digit : queryIP.split("\\:", -1))        if (!isIPv6(digit))          return "Neither";      return "IPv6";    }     return "Neither";  }   private static final String validIPv6Chars = "0123456789abcdefABCDEF";   private boolean isIPv4(final String digit) {    if (digit.isEmpty() || digit.length() > 3)      return false;    if (digit.length() > 1 && digit.charAt(0) == '0')      return false;     for (final char c : digit.toCharArray())      if (c < '0' || c > '9')        return false;     final int num = Integer.parseInt(digit);    return 0 <= num && num <= 255;  }   private boolean isIPv6(final String digit) {    if (digit.isEmpty() || digit.length() > 4)      return false;     for (final char c : digit.toCharArray())      if (!validIPv6Chars.contains("" + c))        return false;     return true;  }}

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