Mega Code Archive
Compares all Strings in an array and returns the initial sequence of characters that is common to all of them
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/*
* Licensed to the Apache Software Foundation (ASF) under one or more
* contributor license agreements. See the NOTICE file distributed with
* this work for additional information regarding copyright ownership.
* The ASF licenses this file to You 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.
*/
public class Main {
/**
* <p>Compares all Strings in an array and returns the initial sequence of
* characters that is common to all of them.</p>
*
* <p>For example,
* <code>getCommonPrefix(new String[] {"i am a machine", "i am a robot"}) -> "i am a "</code></p>
*
* <pre>
* StringUtils.getCommonPrefix(null) = ""
* StringUtils.getCommonPrefix(new String[] {}) = ""
* StringUtils.getCommonPrefix(new String[] {"abc"}) = "abc"
* StringUtils.getCommonPrefix(new String[] {null, null}) = ""
* StringUtils.getCommonPrefix(new String[] {"", ""}) = ""
* StringUtils.getCommonPrefix(new String[] {"", null}) = ""
* StringUtils.getCommonPrefix(new String[] {"abc", null, null}) = ""
* StringUtils.getCommonPrefix(new String[] {null, null, "abc"}) = ""
* StringUtils.getCommonPrefix(new String[] {"", "abc"}) = ""
* StringUtils.getCommonPrefix(new String[] {"abc", ""}) = ""
* StringUtils.getCommonPrefix(new String[] {"abc", "abc"}) = "abc"
* StringUtils.getCommonPrefix(new String[] {"abc", "a"}) = "a"
* StringUtils.getCommonPrefix(new String[] {"ab", "abxyz"}) = "ab"
* StringUtils.getCommonPrefix(new String[] {"abcde", "abxyz"}) = "ab"
* StringUtils.getCommonPrefix(new String[] {"abcde", "xyz"}) = ""
* StringUtils.getCommonPrefix(new String[] {"xyz", "abcde"}) = ""
* StringUtils.getCommonPrefix(new String[] {"i am a machine", "i am a robot"}) = "i am a "
* </pre>
*
* @param strs array of String objects, entries may be null
* @return the initial sequence of characters that are common to all Strings
* in the array; empty String if the array is null, the elements are all null
* or if there is no common prefix.
* @since 2.4
*/
public static String getCommonPrefix(String[] strs) {
if (strs == null || strs.length == 0) {
return "";
}
int smallestIndexOfDiff = indexOfDifference(strs);
if (smallestIndexOfDiff == -1) {
// all strings were identical
if (strs[0] == null) {
return "";
}
return strs[0];
} else if (smallestIndexOfDiff == 0) {
// there were no common initial characters
return "";
} else {
// we found a common initial character sequence
return strs[0].substring(0, smallestIndexOfDiff);
}
}
/**
* <p>Compares all Strings in an array and returns the index at which the
* Strings begin to differ.</p>
*
* <p>For example,
* <code>indexOfDifference(new String[] {"i am a machine", "i am a robot"}) -> 7</code></p>
*
* <pre>
* StringUtils.indexOfDifference(null) = -1
* StringUtils.indexOfDifference(new String[] {}) = -1
* StringUtils.indexOfDifference(new String[] {"abc"}) = -1
* StringUtils.indexOfDifference(new String[] {null, null}) = -1
* StringUtils.indexOfDifference(new String[] {"", ""}) = -1
* StringUtils.indexOfDifference(new String[] {"", null}) = 0
* StringUtils.indexOfDifference(new String[] {"abc", null, null}) = 0
* StringUtils.indexOfDifference(new String[] {null, null, "abc"}) = 0
* StringUtils.indexOfDifference(new String[] {"", "abc"}) = 0
* StringUtils.indexOfDifference(new String[] {"abc", ""}) = 0
* StringUtils.indexOfDifference(new String[] {"abc", "abc"}) = -1
* StringUtils.indexOfDifference(new String[] {"abc", "a"}) = 1
* StringUtils.indexOfDifference(new String[] {"ab", "abxyz"}) = 2
* StringUtils.indexOfDifference(new String[] {"abcde", "abxyz"}) = 2
* StringUtils.indexOfDifference(new String[] {"abcde", "xyz"}) = 0
* StringUtils.indexOfDifference(new String[] {"xyz", "abcde"}) = 0
* StringUtils.indexOfDifference(new String[] {"i am a machine", "i am a robot"}) = 7
* </pre>
*
* @param strs array of strings, entries may be null
* @return the index where the strings begin to differ; -1 if they are all equal
* @since 2.4
*/
public static int indexOfDifference(String[] strs) {
if (strs == null || strs.length <= 1) {
return -1;
}
boolean anyStringNull = false;
boolean allStringsNull = true;
int arrayLen = strs.length;
int shortestStrLen = Integer.MAX_VALUE;
int longestStrLen = 0;
// find the min and max string lengths; this avoids checking to make
// sure we are not exceeding the length of the string each time through
// the bottom loop.
for (int i = 0; i < arrayLen; i++) {
if (strs[i] == null) {
anyStringNull = true;
shortestStrLen = 0;
} else {
allStringsNull = false;
shortestStrLen = Math.min(strs[i].length(), shortestStrLen);
longestStrLen = Math.max(strs[i].length(), longestStrLen);
}
}
// handle lists containing all nulls or all empty strings
if (allStringsNull || (longestStrLen == 0 && !anyStringNull)) {
return -1;
}
// handle lists containing some nulls or some empty strings
if (shortestStrLen == 0) {
return 0;
}
// find the position with the first difference across all strings
int firstDiff = -1;
for (int stringPos = 0; stringPos < shortestStrLen; stringPos++) {
char comparisonChar = strs[0].charAt(stringPos);
for (int arrayPos = 1; arrayPos < arrayLen; arrayPos++) {
if (strs[arrayPos].charAt(stringPos) != comparisonChar) {
firstDiff = stringPos;
break;
}
}
if (firstDiff != -1) {
break;
}
}
if (firstDiff == -1 && shortestStrLen != longestStrLen) {
// we compared all of the characters up to the length of the
// shortest string and didn't find a match, but the string lengths
// vary, so return the length of the shortest string.
return shortestStrLen;
}
return firstDiff;
}
}
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