折半查找

折半查找

一 、非递归法

package com.DS.search.bisearch;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * @Name：  折半查找 非递归法
 * @Author：ZYJ
 * @Date：2019-08-10-11:38
 * @Description:
 */
public class biSearchTest {
    public static void main(String[] args) throws IOException {
        int[] arr ={3,7,8,12,14,16,19};
        System.out.print("请输入要查找的数字：");
        BufferedReader buf = new BufferedReader(new InputStreamReader(System.in));
        int value = Integer.parseInt(buf.readLine());
        int result = BinarySearch(arr,value);
        if (result==-1){
            System.out.println("没有找到该数！");
        }else {
            System.out.println(value+"的索引为："+result);
        }
    }

    public static int BinarySearch(int[] arr,int value){
        int left =0;
        int right = arr.length-1;
        while (left<=right){
            int mid = (left +right)/2;
            if(value==arr[mid]){
                return mid;
            }else if(value<arr[mid]){
                right=mid-1;
            }else {
                left=mid+1;
            }
        }
      return -1;
    }
}

二、递归法

package com.DS.search.bisearch;

import java.io.BufferedReader;
import java.io.IOException;
import java.io.InputStreamReader;

/**
 * @Name：折半查找 递归法
 * @Author：ZYJ
 * @Date：2019-08-10-15:44
 * @Description:
 */
public class BinarySearch {
    public static void main(String[] args) throws IOException {
        int[] arr = {13,15,27,35,43,61,72};
        System.out.print("请输入要查找到的数：");
        BufferedReader buf = new BufferedReader(new InputStreamReader(System.in));
        int value =Integer.parseInt(buf.readLine());
        int result = BinarySearch(arr,value);
        if(result==-1){
            System.out.println("该数字不存在！！！");
        }else {
            System.out.println(value+"的索引是："+result);
        }
    }

    public static int BinarySearch(int[] arr ,int value){
        int left = 0;
        int right = arr.length-1;
        return BinarySearch(arr,value,left,right);
    }
    
    public static int BinarySearch(int[] arr,int value,int left,int right){
        if(left<right){
            return -1;
        }
        int mid = (left+right)/2;
        if(value==arr[mid]){
            return mid;
        }else if(value<arr[mid]){
            return BinarySearch(arr,value,left,mid-1);
        }else {
            return BinarySearch(arr,value,left=mid+1,right);
        }
    }
}