Given an array of integers as input, return true if the array is sorted. Note that the array can be sorted in either ascending or descending order

Question

Sample Input #1

isSorted([1,3,5,7})

Sample Output #1

true

Sample Input #2

isSorted({11,9,2,-5})

Sample Output #2

true

Sample Input #3

isSorted({1,2,3,4,-1,-2})

public boolean isSorted(int[] arr){

    boolean isSorted = false;
    if(arr.length==1)
    return true;

    for(int i=0;i<arr.length-1;i++)
    {

        if(arr[i]<arr[i+1])
        {
            isSorted = true;
        }
        else if(arr[i]>arr[i+1])
        {
            isSorted = true;
        }
        else
            isSorted = false;

        if(isSorted != true)
            return isSorted;
    }
    return isSorted;
}

What happens to my code some of my testcase didn't pass parameter '{24,27,30,31,34,37,40,42}' pass parameter '{1,3,5,7,4}' fail

Answer 1

You are trying to use a single boolean variable to keep two bits of information, which does not work. You need two boolean s here - one to indicate that the array is sorted in ascending order, and another one to indicate that the array is sorted in descending order.

Prepare two variables, isAscending = true and isDescending = true . Go through the array the way you do now, and set the corresponding variable to false if you detect an inversion. Never set these variables to true again, because a single inversion breaks the sort order.

if (arr[i]<arr[i+1]) isDescending = false;
if (arr[i]>arr[i+1]) isAscending = false;

That's all you need to do. Once the loop is over, isAscending || isDescending isAscending || isDescending expression gives you the answer.

To speed up an exit from your for loop, use this termination condition:

i<arr.length-1 && (isAscending || isDescending)

Answer 2

Logic:

• Loop through list with an index counter
• First, forward index while next two values are equal
• If next value is less than current value, do descending check
• If next value is greater than current value, do ascending check
• Verify that all remaining values are ascending/descending, or equal

Answer 3

I have a different proposition than the one from Andreas :

• Initialize booleans ascending and descending to true
• Store item 0, iterate from item 1. While either or the booleans is true, store the current value and increment the index. During each loop, update the two booleans (for example for the first one : ascending = ascending && previousElement <= currentElement
• return ascending || descending ascending || descending

Answer 4

You need another var to indicate the sorting:ascending or descending

short srt = 0;//-1 descending, +1ascending

then compare the two first val to decide the sorting sense, so I propose this solution:

public boolean isSorted(int[] arr){

short srt = 0;//-1 descending, +1ascending

if(arr.length <= 2)
    return true;
else {
    if(arr[0] < arr[1])
        srt = 1;
    else
        srt = -1

for(int i=1;i<arr.length-1;i++)
    if((arr[i] < arr[i+1] && srt = -1) || (arr[i] > arr[i+1] && srt = 1)
        return false;
}
return true;

}