二分法查找

二分法查找：当数据量很大适宜采用该方法。采用二分法查找时，数据需是排好序的。
二分查找时间复杂度 O(logn)

/**
 * 二分法查找,数据需要有序不重复
 */
public class DichotomySearch {
    public static void main(String[] args) {
        int[] arr = {11,22,33,44,55,66,77,88,99};
        System.out.println("88 = " + search(arr, 88)); //7
        System.out.println("44 = " + search(arr, 44));  //3
        System.out.println("100 = " + search(arr, 100));//-1
    }   
    //二分法查找
    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;
    }
}