注意必須是排好序的數組

方法一：

public static int binarySearch(int[] array,int n){
		int start=0;
		int end=array.length-1;
		int middle=(start+end)/2;
		while(start<=end){
			if(n>array[middle]){
				start=middle+1;
			}else if(n<array[middle]){
				end=middle-1;
			}else{
				return middle;
			}
		}
		return -1;
	}

方法二：遞歸

/**
	 * 遞歸寫法
	 * @param array
	 * @param n
	 * @param start
	 * @param end
	 * @return
	 */
	public static int binarySearch(int[] array,int n,int start,int end){
		int middle=(start+end)/2;
		if(n>array[end] || n<array[start] || start>end){
			return -1;
		}
		if(n>array[middle]){
			return binarySearch(array, n, middle+1, end);
		}else if(n<array[middle]){
			return binarySearch(array, n, start, middle-1);
		}else{
			return middle;
		}
	}