折半

[java]代码库

package com.bdqn.yingyun;

public class ZheBan {
	public static void main(String[] args) {
		// 数组必须是有序的数组，且数字不能重复
		int[] arr = { 1, 4, 5, 25, 35, 33, 76 };
		int index = halfindex(arr, 8);
		System.out.println("index=" + index);
	}
	//比较好用些
	public static int halfindex(int[] arr, int key) {
		int min, mid, max;
		min = 0;
		max = arr.length - 1;
		while (min <= max) {
			mid = (min + max) / 2;
			if (key > arr[mid])
				min = mid + 1;
			else if (key < arr[mid])
				max = mid - 1;
			else
				return mid;
		}
		return -1;
	}

/*	public static int halfindex_2(int[] arr, int key) {
		int min, mid, max;
		min = 0;
		max = arr.length - 1;
		mid = (min + max) / 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 = (min + max) / 2;
			
		}
		return mid;
	}*/
}