二分搜索模拟器

如何解决二分搜索模拟器

为什么我的程序不起作用？这是我的代码...

public class Binary {
public static void main(String[] args) {
    ArrayList<Integer> targets = new ArrayList<Integer>();
    
    for (int x = 0; x < 500; x++) {
        int rand = rand();
        targets.add(rand);
    }
    
    ArrayList<Integer> numbers = new ArrayList<Integer>();
    
    for (int x = 0; x < 5000; x++) {
        numbers.add(x);
    }
    
    ArrayList<Integer> comparisons = new ArrayList<Integer>();
    
    for (Integer x : targets) {
        comparisons.add(binary(numbers,x));
    }
    
    int total = 0;
    for (int z = 0; z < 500; z++) {
        total += comparisons.get(z);
    }
    
    int max = comparisons.get(0);
    for (int z = 1; z < 500; z++) {
        if (comparisons.get(z) >= max) {
            max = comparisons.get(z); 
        }
    }
    
    int min = comparisons.get(0);
    for (int z = 1; z < 500; z++) {
        if (comparisons.get(z) <= max) {
            min = comparisons.get(z); 
        }
    }
    
    System.out.println("The average number of comparisons was...     " + total / 500);
    System.out.println("The minimum number of comparisons was...     " + min);
    System.out.println("The maximum number of comparisons was...     " + max);
}

public static int rand() {
    
    int x = (int) (Math.random() * 5000); 
    return x;
}

public static int binary(List<Integer> arr,int target) {
    if (arr.get(arr.size() - 1) == target) {
        return 1; 
    }
    else if (arr.get(arr.size() - 1) < target) {
        return 1 + binary(arr.subList(arr.size() / 2 + 1,arr.size()),target);
    }
    else {
        return 1 + binary(arr.subList(0,arr.size() / 2 + 1),target);
    }
}

}

这是错误信息...

Exception in thread "main" java.lang.indexoutofboundsexception: Index: -1,Size: 0
at java.util.ArrayList$SubList.rangeCheck(ArrayList.java:1227)
at java.util.ArrayList$SubList.get(ArrayList.java:1044)
at marcoB.Binary.binary(Binary.java:58)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:62)
at marcoB.Binary.binary(Binary.java:65)
at marcoB.Binary.main(Binary.java:24)

好像说明第24行有问题：comparisons.add(binary(numbers,x));

我不明白为什么这会导致问题。还有多条其他类似的行，但 eclipse 没有发出任何这些行的错误信号。如果有人有任何建议或可以发现我犯的错误，请告诉我。

非常感谢。

解决方法

您的二进制方法没有检查以停止输入数组是否为空 - 例如，如果 arr 的大小为 1，则 arr.subList(arr.size() / 2 + 1,arr.size()) 将为空数组。在开始时添加这样的简单检查二进制方法应该可以解决您的问题

if (arr.size() == 0) return 1;