二分查找

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今天,我学习了二分查找

得益于二分查找的实现原理,它的效率很高

在使用二分查找前,需要对数组进行排序

实现原理是这样子的:

假如我们要查找数组中其和为指定数字的两个元素

我们先检测0下标和最后一个下标的和

如果等于就输出,大于就把right 的index左移一半,小于就右移一半,就这样不断递归调用(注意栈溢出)

描述起来有点抽象,我们直接上代码

import java.security.PublicKey;import java.util.Arrays;import java.util.Scanner;public class main {/** * @param args */public static void main(String[] args) {int count;int sum;int [] numArry;// TODO Auto-generated method stubScanner scanner=new Scanner(System.in);sum=scanner.nextInt();count=scanner.nextInt();numArry=new int[count];for(int i=0;i<count;i++){numArry[i]=scanner.nextInt();}Arrays.sort(numArry);half_search(numArry, 0, numArry.length-1, sum);//public static void halfsearch (int [] arry , int left,int right,int middle){////}}private static void half_search(int [] numArry,int left,int right,int sum) {// TODO Auto-generated method stub/*right=(numArry.length-1-left)/2;*///错误判断 if(numArry.length==0||numArry==null||sum>numArry[numArry.length-1]){System.out.print("error");}else if(right==left+1&&numArry[left]+numArry[right]!=sum){half_search(numArry, left+1, numArry.length-1, sum);}else if(left==numArry.length-1){return;}else if(numArry[left]+numArry[right]>sum){  //如果找到的结果大于要找的值,下标左移System.out.print(left+"=="+right); half_search(numArry, left, right-(right-left)/2, sum);}else if(numArry[left]+numArry[right]<sum){  //如果找到的结果小于要找的值,下标右移half_search(numArry, left, right+(right-left)/2, sum);                                         }else if (numArry[left]+numArry[right]==sum){System.out.print(numArry[left]+"+"+numArry[right]+"\n");left++;half_search(numArry, left, numArry.length-1, sum);}}}

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