Binary search
Binary basic idea of find is: the n elements is divided into two approximately equal portions, to take a [n / 2] x-compared, if x = a [n / 2], is to find x, the algorithm suspension; if XA [ n / 2], as long as the right half of x in the search array a. binary search method is also known as a binary search, which takes full advantage of the relationship between the order of the elements, using sub-conquer strategy, available in the worst case O (log n) to complete the search task. The basic idea is :( assumed here that the array elements are arranged in the ascending order) will be divided into n elements substantially the same number of halves, take a [n / 2] x to be compared with the look, if x = a [n / 2] is to find x, the algorithm terminates; if xa [n / 2], then we as long as the right half of the array a continuing search for x.
/*
* 使用二分查找法的前提：数列是有序的，顺序存储结构 *
*
* 满足条件后采用折半的方式进行判断、查找，
*
* 折半数列，拿数列下标对应的元素与查找对象比较（默认数列为升序 小-->大）
* 个人总结：先折半，再判断，
*
*
*
*
*
*
*/
public class TwoFindWay {
public static void main(String[] args) {
int[]array =new int[] {1,5,7,9,11,20,29,99};//array.length=8
Boss boss =new Boss(array);
System.out.println(boss.find(6));
System.out.println(boss.find(1));
System.out.println(boss.find(99));
}
public static class Boss{
private int[] array;
/*
* 初始化数组
* @param array
*/
public Boss(int array[]) {
this.array=array;
}
/*
*
* 二分查找法的实现
* @param find
* @return
*
*/
public int find(int fd) {
if(array==null) {//空了就返回-1
return -1;
}
/*
* 定义开始结束下标,二分位置；
* @param start,end,mid;
*
*
*
*/
int start=0;
int end =array.length-1;
while(start<=end) {//使用while 在二分位置开始遍历，查找满足的下标元素
int mid =start+(end-start)/2;
if(array[mid]==fd) {
return mid;//找到了满足的下标元素返回数列 下标
}else if(fd<array[mid]) {
end =mid-1;//折半后 如果说比数列下标元素小，就左移一位下标，
}else {
start=mid+1;//反之，右移一位，
}
}
return -1;//找不到就返回0，
}
}
}
Advantages: fast,
Disadvantages: use threshold.
