(Java) 检查数组是否有增加的元素
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(Java) Check array for increasing elements
提问by jlss4e
I'm attempting to create a method that checks an array for increasing elements. True should be returned if all the elements are in increasing order. I get an out-of-bounds exception when I compare arr[i+1]. Any ideas on how I can make it work.
我正在尝试创建一个方法来检查数组中的元素是否增加。如果所有元素都按升序排列，则应返回 True。当我比较 arr[i+1] 时，出现越界异常。关于如何使其工作的任何想法。
int[] one = {1,2,3,4,5};
public static boolean isIncreasing(int[]arr)
{
boolean z = false;
for(int i=0; i<arr.length;i++)
{
if(arr[i]<arr[i+1])
{
z = true;
}
}
return z;
}
回答by Owen
Because in a list with nitems there are only n-1gaps between them.
因为在包含n项目的列表中，n-1它们之间只有间隙。
Change to
改成
for (int i=0; i<arr.length-1; i++)
(Also you might want to check whether starting with falseand setting to trueis the right way around).
（此外，您可能还想检查开始false和设置是否true是正确的方法）。
回答by Bohemian
You have two problems:
你有两个问题：
- Your loop is one iteration too long: Because you are checking element
i+1, i needs to finished incrementing one iteration earlier than a usual loop. - Your logic is flawed. Your loop will terminate the first timethe check is true, so this array will pass:
{1, 2, 0}when tested the first iteration tests1 < 2which is true, so return true - this is not what we want)
- 您的循环一次迭代太长：因为您正在检查 element
i+1，所以我需要比通常的循环更早完成一次迭代。 - 你的逻辑有问题。您的循环将在第一次检查为真时终止，因此该数组将通过：
{1, 2, 0}测试时第一次迭代测试1 < 2为真，因此返回真 - 这不是我们想要的）
Fixing these two problems:
解决这两个问题：
int[] one = {1,2,3,4,5};
public static boolean isIncreasing(int[] arr) {
for(int i=0 ; i < arr.length - 1; i++) { // finish at length - 1
if (arr[i] > arr[i+1]) {
return false; // found elements that are out of order - return false
}
}
return true; // nothing out of order found - return true
}
This kind of logic - with an early exit with false on problem and a final return of true - is very common and a good pattern to learn.
这种逻辑——在问题上以 false 提前退出，最终返回 true——非常普遍，是一种很好的学习模式。
回答by Nicolas Modrzyk
I suggest you write your method like this
我建议你这样写你的方法
public static boolean isIncreasing(int[]arr)
{
for(int i=1; i<arr.length;i++)
{
if(arr[i-1]>arr[i])
return false;
}
return true;
}
it will help
我会帮你的
- return the proper result (yours returns true when it should not)
- consider out of bounds
- avoid unnecessary looping
- 返回正确的结果（你的结果不应该返回真）
- 考虑越界
- 避免不必要的循环
回答by wannik
You can use Java 8's IntStream.
您可以使用 Java 8 的 IntStream。
import java.util.stream.IntStream;
public class Test {
public static boolean isIncreasing(int[] a) {
return IntStream.range(1, a.length).reduce(0, (acc, e) -> acc + (a[e - 1] <= a[e] ? 0 : 1)) == 0;
}
}
回答by Swagatika
You get that exception as when (i+1)'s value becomes array.length. For example if you have an array of length 10, the elements indexes will be from 0,1,2...till 9. so either you have to check till i < arr.length - 1or you can modify your logic accordingly.
当 (i+1) 的值变为 array.length 时，您会得到该异常。例如，如果您有一个长度为 10 的数组，则元素索引将从 0,1,2...直到 9。因此您必须检查直到i < arr.length - 1或者您可以相应地修改您的逻辑。
