如何查找 int 数组的索引是否以特定数字结束 Java

Question

我有一项任务是 return 一组以 9 结尾的数字。不要改变剩余数字的顺序。我唯一可以使用的是 for 循环。

一时脑袋有些发麻，不知如何是好。

当我 return 结果时，它 return 作为 int 3991599399。

目前我在考虑如何将结果取出for循环。你能帮我找到一种方法将所有带 9 的数字存储在一个新数组中吗？

    
public int[] leavePrice9(int[] prices) {
        
    for (int i = 0; i < prices.length; i++) {
            int result = prices[i];
            
            if (result % 10 == 9);
    }
}
    public static void main(String[] args) {
        QuadraticEquationSolver shop = new QuadraticEquationSolver();

        //Should be [399, 1599, 399]
        int[] prices = new int[] {399, 1599, 399, 50, 10, 10, 70};
        System.out.println(Arrays.toString(shop.leavePrice9(prices)));
    }
}

Answer 1

您可以使用以下方法getAllWithLastDigit()。它采用 int 和一个数字 (0-9) 的数组，return 是一个新数组，其中包含以该指定数字为最后一位的所有元素。原始数组的元素保持不变，因此显然保留了顺序。

import java.util.*;

public class Application {
    public static void main(String[] args) {
        int[] prices = new int[]{399, 1599, 399, 50, 10, 10, 70};
        System.out.println(Arrays.toString(getAllWithLastDigit(prices, 9)));
    }

    public static int[] getAllWithLastDigit(int[] array, int lastDigit){
        if(lastDigit < 0 || lastDigit > 9) throw new IllegalArgumentException("lastDigit must be between 0 and 9!");
        var lst = new ArrayList<Integer>();
        for (int i = 0; i < array.length; i++) {
            int result = array[i];
            if (result % 10 == lastDigit) lst.add(result);
        }
        // convert array list back to integer array
        return lst.stream().mapToInt(i -> i).toArray();
    }
}

预期输出：

[399, 1599, 399]

这使用 ArrayList 来能够在我们遇到最后一位数字为 9 的元素时动态地将元素添加到列表中。最后，我们需要将列表转换回数组，如您所愿 return 整数数组。

您所做的只是字符串连接，而不是这样做，我们现在将元素添加到列表中，将该列表转换回 int 数组并 return 它。您的实现遗漏了创建新数组和 returned.

的部分

编辑

这里是一个没有使用 ArrayList 的版本。在这里，我们首先创建一个能够容纳最大数量结果的数组，并向其中添加一个结果，同时为每个新元素增加一个 counter。然后我们必须（可能）缩小数组，使其只包含数组中实际元素的数量。为此，我们创建了一个数组的副本，无论结果中有多少元素。

import java.util.*;

public class Application {
    public static void main(String[] args) {
        int[] prices = new int[]{399, 1599, 399, 50, 10, 10, 70};
        System.out.println(Arrays.toString(getAllWithLastDigit(prices, 9)));
    }

    public static int[] getAllWithLastDigit(int[] array, int lastDigit){
        if(lastDigit < 0 || lastDigit > 9) throw new IllegalArgumentException("lastDigit must be between 0 and 9!");
        // create an array which has the same size as the input, this way we guarantee that we have enough space for all result
        int[] elements = new int[array.length];
        // counter of how many elements are in the array 
        int counter = 0;
        for (int i = 0; i < array.length; i++) {
            int result = array[i];
            if (result % 10 == lastDigit) elements[counter++] = array[i];
        }
        // now we need to create a new array which is exactly as long as we need it (if we don't have that already)
        if(counter == array.length) return elements;
        // Alternative: use Java API Arrays.copyOf(elements, counter)
        return copyArray(array, counter);
    }

    public static int[] copyArray(int[] array, int newLength){
        if(newLength < 0) throw new IllegalArgumentException("Length must not be < 0");
        var copy = new int[newLength];
        // make sure we don't go out of bounds because the new array could be longer than the old one
        var until = Math.min(array.length, newLength);
        // copy over all elements
        for (int i = 0; i < until; i++) {
            copy[i] = array[i];
        }
        return copy;
    }
}

Answer 2

这是一个基于 O/P:

代码的版本

public int[] leavePrice9(int[] prices) {
    int count = 0;  // how many prices qualify? 
    int [] result = new int [prices.length]; // hold qualifying prices
    // worst case: every price will qualify.
    // result is large enough to handle worst case
        
    for (int i = 0; i < prices.length; i++) {                               
            if (prices[i] % 10 == 9)
                 result[count++] = prices [i];
    }
    return Arrays.copyOf (result, count);
}
    public static void main(String[] args) {
        QuadraticEquationSolver shop = new QuadraticEquationSolver();

        //Should be [399, 1599, 399]
        int[] prices = new int[] {399, 1599, 399, 50, 10, 10, 70};
        System.out.println(Arrays.toString(shop.leavePrice9(prices)));
    }
}

如何查找 int 数组的索引是否以特定数字结束 Java

How do find if an index of int array ends on a specific digit Java

java

arrays

for-loop

编辑