带有过程输出的二分搜索

Question

预期输出：

如果键低于中点

数据：[1, 4, 6, 13, 14, 23, 30, 45, 58, 67, 76, 89, 99]

输入键：6

二分查找：

1 step index - 0 : 1, not found !

2 step index - 1 : 4, not found !

3 step index - 2 : 6, founded !!

如果键大于中点

数据：[1, 4, 6, 13, 14, 23, 30, 45, 58, 67, 76, 89, 99]

输入键：89

二分查找：

1 step index - 0 : 45, not found !

2 step index - 1 : 58, not found !

3 step index - 2 : 67, not found !

4 step index - 3 : 76, not found !

5 step index - 4 : 89, founded !!

我的输出

如果键低于中点

Index- 1 = 4, data founded !

~~ FINISHED SEARCHED ~~

问题是我无法逐步打印过程。帮我完成代码。

如果key大于中点

Index - 10 = 4, data founded !

~~FINISHED SEARCHED~~

来源

这是我的源代码：

package binarysearch;

import java.util.Scanner;

import java.util.Arrays;

public class BinarySearch {
    
    public static void main(String [] args) throws Exception{
        Scanner input = new Scanner (System.in);
        int[] data = {1, 4, 6, 13, 14, 23, 30, 45, 58, 67, 76, 89, 99};
        boolean again = true;
        String choose;
        while(again == true){
            System.out.println("Data         : "+Arrays.toString(data));
            System.out.print("Input key : ");
            int find = input.nextInt();
            System.out.println("");
            int repeat= 0;
            int start= 0;
            int end= data.length - 1;
            int mid;
            while(start <= end){
                mid= (start+ end) / 2;
                if(find== data[mid]){
                    break;
                }else if(find> data[mid]){
                    start= mid + 1;
                }else{
                    end= mid- 1;
                }   
            }
            if(awal > akhir){
                System.out.println("Index - "+start+" = "+find+", data not founded");
            }else{
                System.out.println("Index - "+start+" = "+find+", data founded !");
            }
            
            System.out.println("~~ FINISHED SEARCHED ~~");
            System.out.println("");
            System.out.print("DO YOU WANT EXIT ? [y] / [x] ? ");
            choose= input.next();
            if(choose.equals("Y") || choose.equals("y")){
                again = true;
            }else if(choose.equals("X") || choose.equals("x")){
                again= false;
                System.exit(0);
                System.out.println("SEARCHING IS FINISHED, THANK YOU");
            }else{
                System.out.println("INVALID INPUT!!");
                again= false;
                System.exit(0);
            }
            System.out.println("");
        }
    }
}

Answer 1

您的代码对我来说似乎很好。重写了一点帮助你调试：

    int[] data = {1, 4, 6, 13, 14, 23, 30, 45, 58, 67, 76, 89, 99};
    int find =  67;
    int start = 0;
    int end= data.length - 1;
    int mid = 0;
    System.out.println("Find - "+find);
    while (start <= end) {
        mid = (start + end) / 2;
        if(find == data[mid]) {
            break;
        } else if(find > data[mid]) {
            start = mid + 1;
        } else {
            end = mid - 1;
        }   
        System.out.println("Index - "+mid+" - val - "+data[mid]+" - not found");
    }

    if (data[mid] == find) {
        System.out.println("Index - "+start+" - val - "+find+", data found");
    } else {
        System.out.println("Data not found");
    }

Answer 2

您的示例看起来不像是二进制搜索算法。因为二进制搜索总是从“搜索区域”的中间开始。考虑阅读以下内容：http://rosettacode.org/wiki/Binary_search。

一个实现：

class BinarySearchRecursive {

    public static int binarySearch(int[] haystack, int needle, int lo, int hi, int step) {
        if (hi < lo) {
            return -1;
        }
        int guess = (hi + lo) / 2;
        if (haystack[guess] > needle) {
            System.out.println("step " + step + " index: " + haystack[guess] + " not found.");
            return binarySearch(haystack, needle, lo, guess - 1, ++step);
        } else if (haystack[guess] < needle) {
            System.out.println("step " + step + " index: " + haystack[guess] + " not found.");
            return binarySearch(haystack, needle, guess + 1, hi, ++step);
        }
        System.out.println("step " + 1 + " index: " + haystack[guess] + " found.");
        return guess;
    }

    public static void main(String[] args) {
        int[] haystack = {1, 4, 6, 13, 14, 23, 30, 45, 58, 67, 76, 89, 99};
        int needle = 6;

        int index = binarySearch(haystack, needle, 0, haystack.length, 0);

        if (index == -1) {
            System.out.println(needle + " is not in the array");
        } else {
            System.out.println(needle + " is at index " + index);
        }
    }
}