Question

我找到了一些可用于对整数数组执行二进制搜索的代码，我正在尝试更改它，以便我可以在字符串数组上使用它。

这是我到目前为止所做的：

import edu.princeton.cs.introcs.In;
import edu.princeton.cs.introcs.StdIn;
import edu.princeton.cs.introcs.StdOut;
import java.util.Arrays;

public class BinarySearch {

    /**
     * This class should not be instantiated.
     */
    private BinarySearch() { }

    /**
     * Searches for the integer key in the sorted array a[].
     * @param key the search key
     * @param a the array of integers, must be sorted in ascending order
     * @return index of key in array a[] if present; -1 if not present
     */
    public static int rank(String key, String[] a) {
        int lo = 0;
        int hi = a.length - 1;
        int steps = 0;
        while (lo <= hi) {

            steps = steps + 1;  // this will keep count of the number of steps needed

            // Key is in a[lo..hi] or not present.
            int mid = lo + (hi - lo) / 2;



            if      (key < a[mid]) 
            {
                hi = mid - 1;
            }
            else if (key > a[mid]) 
            {
                lo = mid + 1;
            }
            else return mid;
        }
        return steps;
    }

    /**
     * Reads in a sequence of integers from the whitelist file, specified as
     * a command-line argument. Reads in integers from standard input and
     * prints to standard output those integers that do *not* appear in the file.
     * @param args
     */
    public static void main(String[] args) {

        // read the integers from a file
        In in = new In("C:\\Users\\Owner\\Desktop\\EnglishWordList.txt");
        String[] whitelist = in.readAllStrings();

        // sort the array
        Arrays.sort(whitelist);

        // read integer key from standard input; print if not in whitelist
        while (!StdIn.isEmpty()) {
            String key = StdIn.readString();
            if (rank(key, whitelist) == -1)
                StdOut.println(key);
        }
    }
}

我在两个if语句的rank（）方法中遇到错误。它声明我不能使用运算符＆＃34;＆lt;＆＃34;和＆＃34;＆gt;＆＃34;对于字符串，意味着它不看ASCII码。我该如何解决这个问题？可能还有其他问题，但这是我的IDE唯一突出的问题。请让我知道你的想法。

Answer 1

您可以使用a.compareTo(b)，即使用可比较的界面，而不是使用>或<运算符。

可比较的界面。比较值并返回一个int，它告诉值是否比较小于，等于或大于。如果您的类对象具有自然顺序，请实现Comparable接口并定义此方法。所有具有自然排序的Java类都实现了这一点（String，Double，BigInteger，...）。

Answer 2

请尝试使用以下算法

public boolean binarySearch(int key, int[] arrayToSearch) {
    if (arrayToSearch.length == 0) {
        return false;
    }
    int low = 0;
    int high = arrayToSearch.length - 1;

    while (low <= high) {
        int midItem = (low + high) / 2;
        if (key > arrayToSearch[midItem]) {
            low = midItem + 1;
        } else if (key < arrayToSearch[midItem]) {
            high = midItem - 1;
        } else { // The element has been found
            return true;
        }
    }
    return false;
}

Answer 3

试试这个，它也适用于字符串

 public static String binarySearch(String[] names, String x) {
        int high = names.length - 1;
        int low = 0;
        int mid = 0;

        while (low <= high) {

            mid = (low + high) / 2;

            if (names[mid].compareTo(x) == 0) {
                return names[mid];
            }
            else if (names[mid].compareTo(x) > 0) {
                high = mid - 1;
            }
            else {
                low = mid + 1;
            }
        }
        return null;
    }

Java：二进制搜索字符串数组

3 个答案: