二分查找

二分查找也称折半查找（Binary Search），它是一种效率较高的查找方法。但是，折半查找要求线性表必须采用顺序存储结构，而且表中元素按关键字有序排列。（百度百科：https://baike.baidu.com/item/二分查找/10628618?fr=aladdin）

public class Test{

	public static void main(String[] args) {

		int src[] = {1, 3, 4, 5, 7, 17, 20, 22, 50};
		for (int a : src) {
			System.out.print(a + ", ");
		}
		System.out.println();
		int dst = new Test().binarySearch(src, 5);
		System.out.println(dst);
		
	}
	
	public int binarySearch(int src[], int dst) {
		int count = src.length;
		int start = 0;
		int end = src.length;
		while(start!= count - 1 && end != 0) {
			int middle = (start + end) / 2;
			if (src[middle] > dst) {
				end = middle;
			} else if (src[middle] < dst) {
				start = middle;
			} else {
				return middle;
			}
		}
		
		// when not existed
		return -1;
	}
}