Java BinarySearch
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; } }
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勿忘初心 方得始终
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