二分法 查找

package com.algorithm;/** * Created by nanzhou on 2017/7/20. */public class Dichotomy {    /**     * 二分法 查找  时间复杂度O(logn)     * @param args     */    public static void main(String[] args) {        int[] arr = new int[]{12, 23, 34, 45, 56, 67, 77, 89, 90};        System.out.println(search(arr, 12));        System.out.println(search(arr, 45));        System.out.println(search(arr, 67));        System.out.println(search(arr, 89));        System.out.println(search(arr, 99));    }    public static int search(int[] arr, int key) {        int start = 0;        int end = arr.length - 1;        while (start <= end) {            int middle = (start + end) / 2;            if (key < arr[middle]) {                end = middle - 1;            } else if (key > arr[middle]) {                start = middle + 1;            } else {                return middle;            }        }        return -1;    }}