折半（二分）查找

使用迭代实现

	/**
	 * 折半查找(二分查找)
	 * @param arr 待查数组
	 * @param key 待查元素
	 * @return 索引
	 */
	public static int binarySearch(int[] arr, int key) {
		int low = 0, heigh = arr.length - 1, mid = 0;
		for (int i = 0, l = arr.length; i < l; i++) {
			mid = (low + heigh) / 2;
			if (key < arr[mid]) {
				heigh = mid - 1;
			} else if (key > arr[mid]) {
				low = mid + 1;
			} else 
				return mid;
		}
		return -1;
	}

使用递归实现

 

	/**
	 * 折半查找(二分查找)
	 * @param arr 待查数组
	 * @param key 待查元素
	 * @param low
	 * @param heigh
	 * @return 索引
	 */
	public static int binarySearch(int[] arr, int key, int low, int heigh) {
		if (low <= heigh) {
			int mid = (low + heigh) / 2;
			if (key < arr[mid]) {
				return binarySearch(arr, key, low, mid - 1);
			} else if (key > arr[mid]) {
				return binarySearch(arr, key, mid + 1, heigh);
			} else if (key == arr[mid]) {
				return mid;
			}
		}
		return -1;
	}