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));

	}
}