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7 votes

pset3: sort -- having trouble connecting all the dots

Where do I implement that? In helpers.c? helpers.h? A library's .h file is a header file. It does NOT contain definitions. Instead, it contains code that declares the library's resources that are ...
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3 votes
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Pset3 Segmentation Fault

One of the skills that are indirectly taught in this class, as well as being one of the most important skills you must learn as a programmer is how to debug a program. You will run into seg faults ...
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3 votes
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Pset3 Search/Find problems

I don't want to sound cruel here, but your sort routine has serious problems. It is incomplete, it has code that appears to serve no purpose ( an if statement with no code to process if true), and ...
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3 votes

pset3 --> bubble sort

The problem is that you are swapping values[i] with values[i+1] while also allowing i to go to a maximum of n-1. Let's say that n=10, so the array has 10 elements, 0 through 9. When the code sorts ...
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3 votes
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Bubble sort - omega or lower bound

In Big O notation and Omega notation the constants are not computed. Say you have an array with 1000 places. It's not that different to say 1000 than 999. So the n-1 becomes n. Also let's say that you ...
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  • 7,326
3 votes

I don't understand how the worst case performance of bubble sort is O(n^2)

Well, the number of iterations you did was basically n + (n - 1) + (n - 2) + ... + 1 Mathematically, this is equal to n (n + 1) / 2 which is equal to n^2 + n / 2 and since we don't care about small ...
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3 votes
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Pset3: Tideman sort_pairs doesn't work?

preferences[pairs[i].winner][pairs[i].loser] > preferences[pairs[i+1].winner][pairs[i+1].loser] This condition swaps the elements in ascending order while check50 checks for the pairs array for ...
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  • 66
2 votes
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<value optimized> GDB self optimizing everything

"This is a bug in clang, which has been fixed in version 3.5. The CS50 team is working on getting an update out with update50." -see link Variable optimized out eventhough it will be used later
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2 votes

Selection sort does not sort the unsorted portion once no swapping position is reached?

The reason why 100 is ignored is because you're comparing values[min] with values[j] only. And since j is initially set to i + 1 which is 1, values[0] is totally ignored. The role of the nested loop ...
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2 votes
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pset 3 GDB: "no executable file specified"

To debug "find" with gdb, enter the following command: gdb find You need to enter the filename of the executable as a parameter following gdb on the command line. Don't use ./ or .c when you enter ...
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2 votes

pset3 find: seg fault (int array won't initialize to 0s)

I used the debugger on it, and it looked perfectly fine. temp[0] to temp[65535] were initially 0. Have you tried using debug50 on it, like ./generate 1000 50|debug50 ./find 127? Maybe the ...
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2 votes
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CS50x helpers.c help with looping

Your sort is essentially correct. It does restart at the beginning of the list each time. The only problem is that it is going beyond the end of the array. The array has n elements, numbered from ...
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1 vote

Pset3 - Code sorts, but does not find the needle using generate

Your sort is flawed, causing it to eject the largest value and add 0 to the list. Look at the printout of the list to confirm. In the first pass through the outer for loop, k=0. This allows i to ...
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1 vote

PSET3 find having trouble. Can someone help?

The array[start] < array[end] is the wrong condition. You want to keep looping as long as the search interval has elements, so use start <= end instead (<= as you chose both start and ...
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1 vote
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CS50 Helpers.C Find Less, No Idea What's Going On

Both search and sort have problems. First, sort isn't complete. It only makes one pass through the list, so it will only bubble sort the largest value to the last position. I suggest a review of the ...
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1 vote

PSET 3, there is nothing happening

Your do..while loop really should be a regular while loop, but it would blow up only if your array to search was empty (then you're accessing values[-1] within the loop). Your condition is wrong. ...
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1 vote
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Segmentation fault for pset3 sorting

The code creates the counter array: int counter[65535]; but doesn't initialize it. What is in the array? Try printing out the contents of the array (or maybe the first 20 elements) ...
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1 vote
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pset3 helpers.c (help)

You are comparing to element values[(n+1)/2], but your recursive calls look like you meant values[n/2] instead, which makes a lot more sense, as n/2 is always the middle element's index, or the higher ...
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1 vote
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Pset 3 sort function won't swap

apparently, you're trying to implement selection sort. the problem appears to be with this condition if (values[j] < values [i]) { min = j; } are you sure you wanna update min every time ...
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1 vote
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'redefinition of i' compilation error pset 3 sort

The syntax for loop consists of ; and not ,. for (int i = 0 ; i < n ; i++) { // your stuff here }
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  • 3,316
1 vote
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Why doesn't my sort algorithm work

Your problem is in your sorting. Check the Wikipedia article about bubble sort implementation: https://en.wikipedia.org/wiki/Bubble_sort#Implementation. In the most non-optimized case, the pseudo-code ...
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  • 7,326
1 vote
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pset3 - find less / sort video availability

The URL should be updated in the spec shortly. Here it is in the meantime: https://www.youtube.com/watch?v=TYnkJckP1Ss
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1 vote
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Pset3 - Find: I can't find what's wrong with my sorting algorithm...?

In search, move the calculation of mid into the loop, and make sure the /2 is outside the parentheses. The sorting algorithm has no potential for an infinite loop, and looks correct. Also, it's ...
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1 vote
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is this function correct? CS50 Pset3 (Find)

There are problems here. First, it only makes one pass through the array, so all it will do is push the largest value to the end. The rest of the list will likely not sort. Next, since i can increase ...
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1 vote
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pset3: sort -- Selection Sort Implementation

Looks like some kind of select sort. For that to work, in the outer loop, before the inner loop, set min to i ("smallest non-sorted element so far is at index i"), and in the inner loop (starting at i+...
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1 vote

pset3: selection sort and binary search

I figured it out. It seems like I didn't manage to swap values[i] and values[min] in selection sort the right way, so I did a bit of researching and saw that I need a third integer to do that. Here is ...
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1 vote

Pset3 - my bubble sort breaks the find function

If the list is not already sorted, you have an infinite loop. the counter variable will be incremented at some point, meaning that the while condition is true. Since counter is only incremented and ...
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1 vote
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is my swap function breaking my bubble sort implementation?

The problem here is that the code only makes one pass through the list. It will bubble the largest element to the end of the list, but then stops. It needs to come back to the beginning and repeat ...
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1 vote
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Help with sorting function

The above code is partially correct. Although the logic seems to be appropriate, it is not efficient. All you have to do is set the value of i as minimum every time you enter the 'i' loop, and then ...
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  • 26
1 vote

pset3 --> bubble sort

Consider what happens, when i = n - 1.
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