二分法，递归和非递归方式 实现（Java）

//时间复杂度：O（logn）

package binarySearch;

public class BinarySearch {

//非递归
public static int binarySearch(int[] a,int goal){
int high = a.length - 1;
int low = 0;
int mid  = 0;
while(low <= high){
mid = (high - low)/2+low;//(high+low)/2容易溢出
if(a[mid] == goal){
return mid;
}
else if(a[mid] < goal){
low = mid +1;
}
else
high = mid - 1;
}
return -1;
}

//递归
public static int binarySearch(int[] a,int low,int high,int goal){
while(low <= high){
int mid = (high - low)/2 + low;
if(a[mid] == goal){
return mid;
}
else if(a[mid] < goal){
return binarySearch(a,mid+1,high,goal);
}
else
return binarySearch(a,low,mid-1,goal);
}
return -1;
}

public static void main(String[] args) {
// TODO Auto-generated method stub
int[] a = {1,2,3,4,5,6,7,8,9};
System.out.println(binarySearch(a,0,a.length - 1,2));

}
}