Java查找

Java查找

一、二分查找

/**
 * <p>Title: HalfSearch</p>
 * <p>Description: </p>
 * @author zsd
 * @date 2020年2月20日
 */
public class HalfSearch {
	
	/**
	 * 主函數
	 * <p>Title: main</p>
	 * <p>Description: 主函數</p>
	 * @param args
	 */
	public static void main(String[] args) {
		int[] arr = newArray();
		int num = searchn(arr, 7);
		System.out.println("查到的數爲：" + num);
	}
	
	/**
	 * 創建一個數組
	 * <p>Title: newArray</p>
	 * <p>Description: 創建一個數組</p>
	 * @return
	 */
	private static int[] newArray() {
		int[] array = new int[] {1, 2, 3, 5, 7, 9 ,10, 14, 16, 20};
		return array;
	}

	/**
	 * 查找
	 * <p>Title: search</p>
	 * <p>Description: 查找</p>
	 * @param arr
	 * @param key
	 * @return
	 */
	private static int search1(int[] arr, int key) {
		int max, min, mid;
		max = arr.length - 1;
		min = 0;
		mid = (max + min) / 2;
		while (arr[mid] != key) {
			if (key > arr[mid]) {
				min = mid + 1; 
			} else if (key < arr[mid]) {
				max = mid - 1;
			}
			if (max < min) {
				return -1;
			}
			mid = (max + min) / 2;
		}
		return mid;
	}

	/**
	 * 查找
	 * <p>Title: search</p>
	 * <p>Description: 查找</p>
	 * @param arr
	 * @param key
	 * @return
	 */
	private static int search2(int[] arr, int key) {
		int max, min, mid;
		max = arr.length - 1;
		min = 0;
		while (min <= max) {
			mid = (max + min) / 2;
			if (key > arr[mid]) {
				min = mid + 1; 
			} else if (key < arr[mid]) {
				max = mid - 1;
			} else {
				return mid;
			}
		}
		return -1;
	}
	
}