Java BinarySearch
/**
* <html>
* <body>
* <P> Copyright 1994-2018 JasonInternational </p>
* <p> All rights reserved.</p>
* <p> Created on 2018年4月10日 上午9:46:32</p>
* <p> Created by Jason</p>
* </body>
* </html>
*/
package cn.ucaner.algorithm.search;
/**
* In computer science, binary search, also known as half-interval search or logarithmic search, is a search algorithm that finds the position of a target value within a sorted array. Binary search
* compares the target value to the middle element of the array; if they are unequal, the half in which the target cannot lie is eliminated and the search continues on the remaining half until it is
* successful or the remaining half is empty.
* <p>
* Worst-case performance O(log n)<br>
* Best-case performance O(1)<br>
* Average performance O(log n)<br>
* Worst-case space complexity O(1)<br>
* <p>
* @see <a href="https://en.wikipedia.org/wiki/Binary_search_algorithm">Binary Search (Wikipedia)</a>
* <br>
* @author Justin Wetherell <phishman3579@gmail.com>
*/
public class BinarySearch {
private static final int SWITCH_TO_BRUTE_FORCE = 200;
private static int[] sorted = null;
// Assuming the array is sorted
public static final int find(int value, int[] array, boolean optimize) {
BinarySearch.sorted = array;
try {
return recursiveFind(value, 0, BinarySearch.sorted.length - 1, optimize);
} finally {
BinarySearch.sorted = null;
}
}
private static int recursiveFind(int value, int start, int end, boolean optimize) {
if (start == end) {
int lastValue = sorted[start]; // start==end
if (value == lastValue)
return start; // start==end
return Integer.MAX_VALUE;
}
final int low = start;
final int high = end + 1; // zero indexed, so add one.
final int middle = low + ((high - low) / 2);
final int middleValue = sorted[middle];
if (value == middleValue)
return middle;
if (value > middleValue) {
if (optimize && (end - middle) <= SWITCH_TO_BRUTE_FORCE)
return linearSearch(value, middle + 1, end);
return recursiveFind(value, middle + 1, end, optimize);
}
if (optimize && (end - middle) <= SWITCH_TO_BRUTE_FORCE)
return linearSearch(value, start, middle - 1);
return recursiveFind(value, start, middle - 1, optimize);
}
private static final int linearSearch(int value, int start, int end) {
for (int i = start; i <= end; i++) {
int iValue = sorted[i];
if (value == iValue)
return i;
}
return Integer.MAX_VALUE;
}
}