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DotRegularExpression.java
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DotRegularExpression.java
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/*
* Copyright (C) 2014 Pedro Vicente Gómez Sánchez.
*
* Licensed under the Apache License, Version 2.0 (the "License");
* you may not use this file except in compliance with the License.
* You may obtain a copy of the License at
*
* http://www.apache.org/licenses/LICENSE-2.0
*
* Unless required by applicable law or agreed to in writing, software
* distributed under the License is distributed on an "AS IS" BASIS,
* WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
* See the License for the specific language governing permissions and
* limitations under the License.
*/
package com.github.pedrovgs.problem34;
import java.util.ArrayList;
import java.util.List;
/**
* Given an array of strings, can you write a method to return return just words that matches with
* a pattern containing the "." regular expression.
*
* @author Pedro Vicente Gómez Sánchez.
*/
public class DotRegularExpression {
/**
* Iterative and recursive solution to solve this problem. The complexity order of this algorithm
* is O(N*M) where N is the number of elements in the input array and M the complexity order of
* the method written below. In space terms the complexity order of this algorithm is O(N) because
* we are using an array to keep the result of the problem.
*/
public String[] evaluate(String[] words, String pattern) {
if (words == null || pattern == null) {
throw new IllegalArgumentException("You can't pass null objects as input.");
}
List<String> result = new ArrayList<String>();
for (String word : words) {
if (matchDotRegularExpression(word, pattern)) {
result.add(word);
}
}
return result.toArray(new String[result.size()]);
}
/**
* The complexity order of this recursive algorithm is O(N) where N is the number of letters in
* the word.
*/
private static boolean matchDotRegularExpression(String word, String pattern) {
if (Math.abs(word.length() - pattern.length()) > 1) {
return false;
} else if (word.isEmpty() && pattern.isEmpty()) {
return true;
} else if (pattern.charAt(0) == '.') {
return matchDotRegularExpression(word.substring(1), pattern.substring(1));
} else {
boolean partialMatch = word.charAt(0) == pattern.charAt(0);
return partialMatch && matchDotRegularExpression(word.substring(1), pattern.substring(1));
}
}
}