How can i check the run time of java program?

Question

I need to check if an array is a sub-array of another bigger array. (find an word(sub-array) in a sentence(array)).

I need to do that in a recursion algorithm. that the run time will be log(n).

the arrays :

        char[] sentence = {'h', 'e', 'l', 'l', 'o', 'w', 'o', 'r', 'l', 'd'};
    char[] word = {'l', 'l', 'o', 'w', 'o', 'r'};
                char [] word = {'t', 'n' , 'p'};

my code:

    static boolean wordFinder(char[] arr, char[] arr2, int l, int i) {

    if (i == arr2.length - 1) {
        return true;
    }
    if (arr[l] == arr2[i]) {
        return wordFinder(arr, arr2, l + 1, i + 1);
    }
    if (l == arr.length - 1) {
        return false;
    }
    return wordFinder(arr, arr2, l + 1, 0);


}

the third array is only for checking the code. (the code works, just need to know the run time).

It is totally unclear for me what is the problem here. What do you mean by "run time"? What does it have to do with those arrays? — Amongalen, Jun 11 '19 at 10:19
@Amongalen i need to check if the second array (char[] word) can be fitted to the first array (char [] sentence). i mean if the sentence is "hello world", and the word is "world". i can fit the word array to the sentence array. implement the word array in the sentence array. and by Run-time I mean . I know there are run time of O(n^2), O(n) , log(n) that symbols the run-time. i want to know what my run time is. O(n) or log(n). — Sufferring, Jun 11 '19 at 10:21
These question have been answered [here](https://stackoverflow.com/questions/5204051/how-to-calculate-the-running-time-of-my-program) — Raymond Toh, Jun 11 '19 at 10:24
Are you actually asking that "is your current implementation complexity is O(log(n)) or other?" — MD Ruhul Amin, Jun 11 '19 at 10:24
@ruhul yes. i am a student and my teacher gave me that as a homework. — Sufferring, Jun 11 '19 at 10:27

score 0 · Answer 1 · answered Jun 11 '19 at 10:26

It sounds like you are interested in testing how long a block of code takes to run. To do that, just record the time before and after in milliseconds, and then subtract the two.

long start_time = System.currentTimeMillis();

...
...

long end_time = System.currentTimeMillis();

System.out.println("Code completed in " + (end_time - start_time) + "milliseconds.");

There's also System.nanoTime() for nanoseconds.

MD Ruhul Amin · Answer 2 · 2019-06-11T10:29:34.753

0

The runtime complexity of your program is O(n*m). Here n is the length or arr and m is the length of arr2 why: because in each recursion, there is actually nested loop in each recursion. One loop to iterate over arr and other is to iterate over arr2 for each element of arr.

Well, minimum complexity would be O(n).

Update: Have a look at this link: check-string-substring-another

edited Jun 11 '19 at 10:29

answered Jun 11 '19 at 10:27

MD Ruhul Amin

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thanks :), can you please give me a hint on how to make it log(n)? – Sufferring Jun 11 '19 at 10:29
@Sufferring did you get your answer? – MD Ruhul Amin Jun 11 '19 at 10:40
i saw the link you sent me. and i didn't understand why he runs a loop to create int j if he starts it at 0.plus he runs a for loop inside a for loop. doesnt it makes the run time complexity to o(n^2)? – Sufferring Jun 11 '19 at 10:48
You need to check if all the element of `arr2` (j, 0 to length) is equal to the elements of `arr` (current position i to i+j). arr[i] == arr2[j] .. arr[i+1] == arr[j+1]... – MD Ruhul Amin Jun 11 '19 at 10:54
but wouldn't it make it o(n^2)? because i am running loop inside a loop.. – Sufferring Jun 11 '19 at 11:19
but i need log(n). or o(n) (if its the minimum complexity as said). – Sufferring Jun 11 '19 at 11:31

How can i check the run time of java program?

2 Answers2