2
votes
Accepted
Week 6: DNA sequence aligning example: Are running times iterative approach and reqursive same?
Recursive with memoization and non-recursive do the same number of computations.
The recursive version however is more complex, memoization requires some check whether the value already has been ...
- 20.9k
2
votes
Accepted
Can't get past step 2 in water.c check50 2016.water water.c?
OK, you are pretty close, just some little syntax errors.
When I try to compile your source code with clang I get the following errors, so let's solve them step by step:
test.c:11:26: error: ...
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2
votes
Accepted
Vigenere-Struggling to understand why garbage values are being printed
If you run the code with key = "bbb" and plaintext ABC, the result is ciphertext:BACBDC. This is a mix of the properly coded BCD and the original ABC, printing alternatingly from each string. This ...
- 68.1k
2
votes
Accepted
Why is my ciphertext printing random values?
Apply the %26 to the sum, not the key. Also, don't forget to apply a shift to the plaintext character (like you did in caesar), and shift the result back.
And finally, non-alphabetic plaintext ...
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2
votes
Accepted
I am ABSOLUTELY STUCK! (mario less)
I tried running your code in the sandbox, resulting in an additional row without any hashes on top of the pyramid (you can see the space between the pyramid and the height prompt). To solve the ...
2
votes
Using submit50 on VSCode
I noticed this a duplicate question that you have already posted here but I can't flag it as a duplicate, so I'll repost my answer here in case anyone chances upon this one instead:
This is due to ...
- 46
2
votes
Accepted
PSET 7 Movies SQL Q9
The issue here was in the syntax of the SQL query. When looking for multiple elements from a subquery, it's necessary to use "IN" in the query. In other words look for all elements A that ...
- 68.1k
2
votes
"cash.c:7:1: error: expected identifier or '('" What do I do?
Get rid of the semicolon on line 6.
A semicolon there marks the line as a function signature. You'll learn more about that later.
- 68.1k
2
votes
Accepted
PSET2 Substitution
Did you remember to add one extra char to the length of ciphertext and to insert the end of string marker in that last space?
Also, shouldn't the length of ciphertext be based on the length of string ...
- 68.1k
2
votes
Accepted
I need help to fix my selection sort code - Practice Problems (Average High Temperatures)
that's a lot of code for a selection sort. It should be able to be sorted without need for a second array and with only two nested for loops.
The setup is pretty straightforward. I'll give a verbal ...
- 68.1k
1
vote
Accepted
One tiny step to completion. Recover recovers all images except the first one. Help!
So let's look at the code that handles the non-signature blocks.
else
{
// if file is open
if (ftell(img) >= 0)
{
fwrite(buffer, 512, 1, img);
...
- 68.1k
1
vote
Accepted
PSet1: Mario - Less Comfortable (Too many periods)
for (space = 0; space <= height - row; space++) runs height - row + 1 times (+1 for having <= instead of <). For the first row, you should have height - 1 spaces, but you have height + 1. Fix ...
- 20.9k
1
vote
Accepted
PSet 3 resize (less)
I'll give you several nudges. Most of the problems arise from the nested for loop structure being off. For example, the current code writes out padding after writing out every pixel. It should only ...
- 68.1k
1
vote
Accepted
Where am I going wrong in Similarities: Substrings?
Check the list extract returns. Its last elements are a bit too short, as there are no len(string) substrings of length num, their number also depends on num itself. You should probably adjust your ...
- 20.9k
1
vote
Accepted
resize : pset3 not all colors are appering after resizing
Let's look at the code that actually processed the image data. (I've refined the style a little to clean it up, but the code is the same.)
for (int i = 0, biHeight = abs(bi.biHeight); i < biHeight;...
- 68.1k
1
vote
Accepted
CS50 Week 4 Recover. Generating 50 Blank images
The biggest problem here is that the code is trying to test for a signature before actually reading in the data from the input file. It's doing a "Ready, Fire, Aim." Order of actions is ...
- 68.1k
1
vote
Accepted
PSET3 Runoff Help Please
To check the name of the candidate in the 1st preferred coloumn only
Remember,
preferences[i][j];
Is simply,
preferences[row][coloumn];
So,
For first preference only
preferences[changing_row][...
- 535
1
vote
PSET3 Runoff Help Please
vote
This function inputs a string a search for the names in the table of candidates, it returns true once the name has been founded or matched i.e == 0
But how?
Use for-loop to iterate through the ...
- 535
1
vote
Accepted
how do i write pesudocode.txt for Mario? (less comfortable)
You make a new file by clicking the green plus sign at the top, next to where it says the name of the file you are currently on. On your keyboard, then do command shift S. It will give you options for ...
- 67
1
vote
are we supposed to use the set from hello.c to begin with Mario (less comfortable) or do we need a new terminal and file?
It's a new program. Start with a new file. You're done with hello.c, but feel free to look at it for any ideas on how to do anything you've done in the past.
These instructions are guiding you through ...
- 68.1k
1
vote
Accepted
are we supposed to use the set from hello.c to begin with Mario (less comfortable) or do we need a new terminal and file?
You don't have to create a new terminal window, but you should only start mario if you're finished with hello. If you're in the hello directory, on your terminal, execute:
cd,
cd pset1,
mkdir mario,
...
- 67
1
vote
Stuck badly in Speller - segmentation fault
node *cursor1 = table[X];
int result = 0;
do
{
result = strcasecmp(word, cursor1->word); // cursor1 is NULL here.
The error messsage:
Memory access error: dereferencing a ...
- 450
1
vote
Counter fails to update for DNA
There's a subtle bug in here:
for char in range(len(tf)):
# ...
char += len(str)-1
Let's say range(len(tf) = [0, 1, 2, 3, 4] and len(str) = 3. What happens if we match while char ...
- 111
1
vote
I am ABSOLUTELY STUCK! (mario less)
You can check your own style by running style50 mario.c
You can see the tests used for grading by clicking the check50 button next to your submission on cs50.me/submissions
With both of those ...
- 18.6k
1
vote
Accepted
Why isn't my key running cyclically?
The code is using a pair of nested for loops. The outer loop cycles through the plaintext while the inner loop cycles through the key. That means that for EACH char in the plaintext, the inner loop ...
- 68.1k
1
vote
CS50 Understanding Technology Grading?? CS50.me?
Generally, you should be receiving grade feedback via email. Perhaps check your spam folders to make sure your feedback hasn't been directed there?
If you can't find it, please send an email to ...
- 18.6k
1
vote
Accepted
CS50 - Pset7 - Quote Redirects To Login - 2017
session.clear() clears the session variables, which holds the user id, which makes @login_required think there is not a logged in user. (Notice the comment before session.clear() in the supplied login ...
- 27.8k
1
vote
Accepted
Lecture Week 6: Dynamic programming: rod example, is the recursion approach correct?
Recursion isn't done right. For example, your function meant to return an int might end without returning anything.
Essence of recursion is that you define a base case (like for example rod of length ...
- 20.9k
1
vote
Accepted
why can't I even log in now ? pset7
Here you replace the string with a dict:
symbol = lookup(symbol)
here you use symbol:
db.execute("UPDATE log SET price=:price, \
total=:total WHERE id=:id AND symbol=:symbol", \
...
- 20.9k
1
vote
Accepted
pset2 crack.c Random Characters Follow When Getting Salt
Where's the end of string marker \0?
printf will keep printing whatever follows in memory until it sees the EOS marker, even into other areas of memory.
If this answers your question, please click ...
- 68.1k
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