思想
折半查找要求较高：
（1）存储节后是数组
（2）数组有序
主要思想是，取中间的记录作为比较对象，假如相等，就返回中间对象的位置，假如小于中间对象，就在左半部分继续查找，否则在右半部分继续查找。
例子
代码
package findMethod;
public class Binserch {
public static void main(String[] args) {
Binserch binserch = new Binserch();
int [] a = {4,5,6,8,9,10};
System.out.println(binserch.search(a, 10));
System.out.println(rank(10, a, 0, a.length-1));
}
public static int rank(int key,int[] arr,int start,int end){
if(start >end){
return -1;
}
int mid=(end+start)/2;
if(key<arr[mid]){
return rank(key,arr,start,mid-1);
}else if(key>arr[mid]){
return rank(key,arr,mid+1,end);
}else{
return mid;
}
}
// 非递归
public int search(int []a,int target){
if (a.length == 0 || a == null) {
return -1;
}
int low = 0;
int high = a.length -1;
int mid = (high + low) /2;
while (low <= high) {
if (a[mid] == target) {
return mid;
}
if (a[mid] > target) {
high = mid -1;
mid = (low + high) /2;
}
if (a[mid] < target) {
low = mid +1;
mid = (low + high) /2;
}
}
return -1;
}
}
