Longest sequence of the same number&how many longest seqeuences exist (without array)

Question

In C, I'm only allowed to use stdio.h and I'm not allowed to use arrays.

The question is: I need to write the function "void MaxLegnth()" that inputs integers as long as they're positive, if it inputs a negative number, the inputting part will stop. I need to find the longest sequence of same numbers, and how many times it occurred. For example:

input:

19 19 97 97 97 97 681 681 681 681 97 36 36 36 97 97 97 97 36 -19

output:

maximum length - 4  
occurred - 3

I've been struggling with this question and came up with this, but I can't figure out how to fix it:

void MaxLength()
{
    int num1, temp, currentmax = 0, countmax = 0, globalmax = 0;
    printf("Please enter positive integers: ");
    scanf_s("%d", &num1);
    temp = num1;
    if (num1 > 0)
        currentmax++;
    while (num1 > 0)
    {
        scanf_s("%d", &num1);
        if (num1 < 0)
        {
            //currentmax--;
            break;
        }
        if (num1 == temp)
        {
            currentmax++;
            temp = num1;
            if (currentmax > globalmax)
                globalmax = currentmax;
        }
        else
        {
            if (currentmax > globalmax)
            {
                globalmax = currentmax;
                countmax = 1;
                currentmax = 1;
                temp = num1;
            }
            if (currentmax < globalmax)
            {
                currentmax = 1;
                temp = num1;
            }
            if (currentmax == globalmax)
                countmax++;
        }

    }
    printf("\ncurrent %d\n", currentmax);
    printf("\nglobal %d\n", globalmax);
    printf("\ncount %d\n", countmax);
}

Sorry for the huge wall of text. Any help would be highly appreciated!

Given your input, is the correct answer is "maximum length - 4 occured - 3" or "maximum length - 4 occured - 2" ? It's the "same number" part that i'm afraid of. Do you have to detect that out of the 3 longest sequence, 2 of them are about the same number ? — Tom's, Mar 20 '18 at 16:32
the occured part refers only to how many times the longest sequence appeared, so whether the sequence is 2 2 2 2 or 4 4 4 4 they're both the longest and they'll both be counted , i hope this cleared your question — Ultraviolence, Mar 20 '18 at 16:35
@IlyaBursov 97 appears 4 times, then 681 appears 4 times, then 97 appears another 4 times. That’s three occurrences of four in a row. — Jonathan Leffler, Mar 20 '18 at 16:40
i think i didn't explain myself properly. it's "occured - 3" because the longest sequence (4 consecutive same number) uccured 3 times, so while 97 97 97 97 and 681 681 681 aren't the same, they're both the longest sequence and both will be counted, sorry for wording myself badly — Ultraviolence, Mar 20 '18 at 16:41
If one of the answers solved your problem, you should [accept an answer](https://stackoverflow.com/help/accepted-answer), not put "solved" in the title. — dbush, Mar 20 '18 at 17:37
@Ultraviolence You are margek as the best the very bad code. — Vlad from Moscow, Mar 21 '18 at 11:31

Iłya Bursov · Accepted Answer · 2018-03-23T06:11:42.143

0

Here is fixed version of your function with some comments:

int num = 0, curr = -1, currCnt = 0, maxCnt = 0, maxCntCnt = 0;
printf("Please enter positive integers: ");
while (num >= 0) {
    if (scanf("%d", &num) != 1) 
        break;
    if (num <= 0)
        break;
    if (num == curr) {
        currCnt++; // new number is continuation of sequence, increase counter
        if (currCnt == maxCnt) {
            maxCntCnt++; // we're reached previously detected max, increase counter
        }
        if (currCnt > maxCnt) {
            maxCnt = currCnt; // we're reached new max, reset counter
            maxCntCnt = 1;
        }
    } else {
        curr = num; // start of new sequence detected, reset counter
        currCnt = 1;
    }
}

printf("\nmaximum length - %d\n", maxCnt);
printf("occured - %d\n", maxCntCnt);

edited Mar 23 '18 at 06:11

answered Mar 20 '18 at 16:48

Iłya Bursov

23,342
4
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@Ultraviolence This function is unsafe. – Vlad from Moscow Mar 20 '18 at 17:38
@VladfromMoscow what exactly is unsafe? – Iłya Bursov Mar 21 '18 at 00:48
@IlyaBursov For starters 0 is not a positive number. Secondly the code is invalid when the user presses Ctrl+Z or Ctrl + d. – Vlad from Moscow Mar 21 '18 at 11:30

Vlad from Moscow · Answer 2 · 2018-03-21T12:58:23.570

0

We beginners should help each other.:)

For starters take into account that the function shall be declared (when the declaration is also a function definition) like

void MaxLength( void )
                ^^^^^
{
    //...
}

Your function is too complicated.

Here is a solution that I can suggest.

#include <stdio.h>

void MaxLength( void )
{
    size_t max_length = 0, max_count = 0;
    int prev_number = 0;

    size_t n = 0;
    _Bool valid_input;

    printf( "Please enter positive integers: " );

    do
    {
        int number = 0;

        valid_input = scanf( "%d", &number ) == 1 && number > 0;

        if ( !valid_input || number != prev_number )
        {
            if ( max_length < n )
            {
                max_length = n;
                max_count  = 1;
            }
            else if ( valid_input && max_length == n )
            {
                max_count++;
            }

            prev_number = number;
            n = 1;
        }
        else
        {
            ++n;
        }

    } while ( valid_input );

    printf( "\nmaximum length - %zu\n", max_length );
    printf( "occured - %zu\n", max_count ); 
}

int main(void) 
{
    MaxLength();

    return 0;
}

The program output is

Please enter positive integers: 19 19 97 97 97 97 681 681 681 681 97 36 36 36 97 97 97 97 36 -19

maximum length - 4
occured - 3

edited Mar 21 '18 at 12:58

answered Mar 20 '18 at 16:50

Vlad from Moscow

301,070
26
186
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thank you so much for your time into writing all this, for some reason though it gives me a runtime error ,it says we used something not initialized. – Ultraviolence Mar 20 '18 at 16:59
That's "prev_number". Initializing at something negative should do the trick. – Tom's Mar 20 '18 at 17:07
@Ultraviolence Initialize prev_number with 0. See my updated post. – Vlad from Moscow Mar 20 '18 at 17:30
@Tom's Or it can be initialized by 0. – Vlad from Moscow Mar 20 '18 at 17:32
Yes, it doesn't matter in the end. – Tom's Mar 20 '18 at 17:32
@Ultraviolence Only my function implementation is correct and safe.:) – Vlad from Moscow Mar 20 '18 at 17:39
... Care to explain why ? Because with wath you say on the other answer, you seem to be a big troll ... – Tom's Mar 21 '18 at 08:09
This function doesn't seem to act correctly (aka "it's bugged"). If I give a negative number rigth away, it say that the maximum len is 0 and it has occured 1 time. How can something that doesn't exist can have occured one time ? – Tom's Mar 21 '18 at 12:49

Tom's · Answer 3 · 2018-03-21T13:09:44.007

0

since everybody give the answer, here's mine :

void MaxLength(void)
{
    int inputNumber;
    int previousNumber = -1;
    int currentLen     = 0;
    int maxLen         = 0;
    int nbMaxLen       = 0; 

    printf("Please enter positive integers: ");
    while (scanf("%d", &inputNumber) == 1 && inputNumber > 0) {
        ++currentLen;
        if (inputNumber != previousNumber) {
            if (currentLen == maxLen) {
                ++nbMaxLen;
            } else if (currentLen > maxLen) {
                maxLen = currentLen;
                nbMaxLen = 1;
            }
            currentLen = 1;
        }
        previousNumber = inputNumber;
    }

    if (currentLen == maxLen) {
        ++nbMaxLen;
    } else if (currentLen > maxLen) {
        maxLen = currentLen;
        nbMaxLen = 1;
    }

    printf("maxLen   = %d\n", maxLen);
    printf("nbMaxLen = %d\n", nbMaxLen);
}

Your problem come from there are minor error across the while loop, like the fact that if currentmax == globalmax, then temp1 will not take num1 value, and I don't think this is what is supposed to do.

Globally, we have the same algorithm, but do not hesitate to ask questions if you found something suspicious.

edited Mar 21 '18 at 13:09

answered Mar 20 '18 at 17:06

Tom's

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thanks alot for helping, more ideas are always welcome! – Ultraviolence Mar 20 '18 at 17:07
@Ultraviolence The function in this post is wrong.:) – Vlad from Moscow Mar 20 '18 at 17:37
For what input ? I tested it with your example and some other, and it seemed to work fine (even when no input is given). – Tom's Mar 21 '18 at 08:07
@Tom's The code is invalid. It does not process the case when the user presses Ctrl + Z or Crel + d. In this case the last sequence will not be counted. – Vlad from Moscow Mar 21 '18 at 11:31
??? Can you stop trolling please ? Either I really missed something, or it's embarrassing to see a 134k rep guy saying thing like that. First, your function doesn't manage ctrl z / ctrl d. Second, YOUR functon is bugged. If I give "-4" rigth away, it say that the maximum len is 0 and it has occured 1 time. How can something that doesn't exist can have occured one time ???? Finally, managing ctrl z / ctrl d while doing scanf will require more step than you think : it will be OS dependant and a big headache for nothing. The user have to press "enter" to input a number. ctrl d is not "enter" ... – Tom's Mar 21 '18 at 12:44

Longest sequence of the same number&how many longest seqeuences exist (without array)

3 Answers3