Java實現二分查找

public class TestSearch {

	public static void main(String[] args) {
		// 數組必需是有序的
		int array[] = {3,6,10,12,25,48,50,56,88,100,102,106,109,220};
		System.out.println(search(array, 25));
		System.out.println(search(array, 0, array.length - 1, 48));
		System.out.println(search(array, 0, array.length - 1, 10000)); 
	}

	/**
	 * 遞歸查找
	 * 
	 * @param array 數組
	 * @param startIndex 開始位置
	 * @param endIndex 結束位置
	 * @param key 查找的數字
	 * @return 數組下標,沒有返回-1
	 */
	public static int search(int array[], int startIndex, int endIndex, int key) {
		int middle = (endIndex - startIndex) / 2 + startIndex;
		if(startIndex >endIndex){
			return -1;
		}
		if (array[middle] == key) {
			return middle;
		} else if (key > array[middle]) {
			return search(array, middle + 1, endIndex, key);
		} else if (key < array[middle]) {
			return search(array, startIndex, middle - 1, key);
		}
		return -1;
	}

	/**
	 * while循環查找
	 * 
	 * @param array 數組
	 * @param key 查找的數字
	 * @return 數組下標,沒有返回-1
	 */
	public static int search(int[] array, int key) {
		int startIndex = 0;
		int endIndex = array.length - 1;
		while (startIndex <= endIndex) {
			int middle = (startIndex + endIndex) / 2;
			if (key == array[middle]) {
				return middle;
			} else if (key < array[middle]) {
				endIndex = middle - 1;
			} else {
				startIndex = middle + 1;
			}
		}
		return -1;
	}
}

運行後：

4
5
-1