Perform a binary search over a sorted list for the given key.

Description

Demo Code

/*/*from www. ja v a 2  s . c  o m*/
 * Copyright (c) 2002-2015, JIDE Software Inc. All rights reserved.
 * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
 *
 * This code is free software; you can redistribute it and/or modify it
 * under the terms of the GNU General Public License version 2 only, as
 * published by the Free Software Foundation.  Oracle designates this
 * particular file as subject to the "Classpath" exception as provided
 * by Oracle in the LICENSE file that accompanied this code.
 *
 * This code is distributed in the hope that it will be useful, but WITHOUT
 * ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
 * FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License
 * version 2 for more details (a copy is included in the LICENSE file that
 * accompanied this code).
 *
 * You should have received a copy of the GNU General Public License version
 * 2 along with this work; if not, write to the Free Software Foundation,
 * Inc., 51 Franklin St, Fifth Floor, Boston, MA 02110-1301 USA.
 */
//package com.java2s;

import java.util.List;

public class Main {
    public static void main(String[] argv) throws Exception {
        List a = java.util.Arrays.asList("asdf", "java2s.com");
        Object key = "java2s.com";
        System.out.println(binarySearch(a, key));
    }

    /**
     * Perform a binary search over a sorted list for the given key.
     *
     * @param a   the array to search
     * @param key the key to search for
     * @return the index of the given key if it exists in the list, otherwise -1 times the index value at the insertion
     *         point that would be used if the key were added to the list.
     */
    @SuppressWarnings("unchecked")
    public static int binarySearch(List<Object> a, Object key) {
        int x1 = 0;
        int x2 = a.size();
        int i = x2 / 2, c;
        while (x1 < x2) {
            if (!(a.get(i) instanceof Comparable)) {
                return i;
            }
            c = ((Comparable) a.get(i)).compareTo(key);
            if (c == 0) {
                return i;
            } else if (c < 0) {
                x1 = i + 1;
            } else {
                x2 = i;
            }
            i = x1 + (x2 - x1) / 2;
        }
        return -1 * i;
    }

    /**
     * Perform a binary search over a sorted array for the given key.
     *
     * @param a   the array to search
     * @param key the key to search for
     * @return the index of the given key if it exists in the array, otherwise -1 times the index value at the insertion
     *         point that would be used if the key were added to the array.
     */
    @SuppressWarnings("unchecked")
    public static int binarySearch(Object[] a, Object key) {
        int x1 = 0;
        int x2 = a.length;
        int i = x2 / 2, c;
        while (x1 < x2) {
            if (!(a[i] instanceof Comparable)) {
                return i;
            }
            c = ((Comparable) a[i]).compareTo(key);
            if (c == 0) {
                return i;
            } else if (c < 0) {
                x1 = i + 1;
            } else {
                x2 = i;
            }
            i = x1 + (x2 - x1) / 2;
        }
        return -1 * i;
    }

    /**
     * Perform a binary search over a sorted array for the given key.
     *
     * @param a   the array to search
     * @param key the key to search for
     * @return the index of the given key if it exists in the array, otherwise -1 times the index value at the insertion
     *         point that would be used if the key were added to the array.
     */
    public static int binarySearch(int[] a, int key) {
        return binarySearch(a, key, 0, a.length);
    }

    /**
     * Perform a binary search over a sorted array for the given key.
     *
     * @param a     the array to search
     * @param key   the key to search for
     * @param start the start index to search inclusive
     * @param end   the end index to search exclusive
     * @return the index of the given key if it exists in the array, otherwise -1 times the index value at the insertion
     *         point that would be used if the key were added to the array.
     */
    public static int binarySearch(int[] a, int key, int start, int end) {
        int x1 = start;
        int x2 = end;
        int i = x2 / 2;
        while (x1 < x2) {
            if (a[i] == key) {
                return i;
            } else if (a[i] < key) {
                x1 = i + 1;
            } else {
                x2 = i;
            }
            i = x1 + (x2 - x1) / 2;
        }
        return -1 * i;
    }
}
Perform a binary search over a sorted list for the given key. - Java java.util

Description

Demo Code

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