binary search

binary search in sorted array:

 

package me.util.algorithm;

/**
 * binary search util
 * @author eric
 * @date 2010-8-29 下午07:09:41
 */
public class BinarySearchUitl {

	public static void main(String[] args) {
		int[] is = new int[] { -10, -9, -9, -5, -4, -3, -3, -2, -1, 0, 1, 2, 5, 6, 7, 8, 9, 11, 14 };
		System.out.println(locateNumInSortedArray(-5, is));
		System.out.println(locateNumInSortedArray(4, is));
	}

	/**
	 * locate num in a sorted array
	 * @param num number to locate
	 * @param arr sorted array in asc order
	 * @return index of the num in array.If not find,-1 will be return.
	 */
	public static int locateNumInSortedArray(int num, int[] arr) {
		if (arr.length == 0 || arr[0] > num || arr[arr.length - 1] < num) {
			return -1;
		}

		int startIndex = 0, endIndex = arr.length - 1;
		while (startIndex <= endIndex) {
			int middleIndex = (startIndex + endIndex) >> 1;
			if (num == arr[middleIndex]) {
				return middleIndex;
			} else if (num > arr[middleIndex]) {
				startIndex = middleIndex + 1;
			} else {
				endIndex = middleIndex - 1;
			}
		}
		return -1;
	}
}