I am new here. I'm trying a C# problem on Leetcode about Longest Common Prefix. I know this problem has been solved MANY times. I'm just having a hard time understanding why my code doesn't work under certain conditions. When the input ["flower","flow","flight"] is put in, it works just fine and get the output "fl". However, when I get to the input ["ab", "a"], I suddenly get an IndexOutOfRangeException. Anyone know why? Here's my code:
public class Solution {
public string LongestCommonPrefix(string[] strs) {
StringBuilder sb = new StringBuilder();
int h = 1;
int count = 0;
if (strs.Length == 1){
return strs[0];
}
for (int i = 0; i<strs[0].Length; i++)
{
if ((strs[0])[i].Equals((strs[h])[i])){
count++;
if (h<strs.Length-1){
h++;
}
}
}
for (int j = 0; j < count; j++)
{
sb.Append((strs[0])[j]);
}
return sb.ToString();
}
}
You can debug by making a simple console app in Visual Studio. I added a Console.Writeline(strs[0] + strs[h]) to your code to demonstrate the logic as is. Running your code in debug, you can step through and see where the exception gets thrown:
Notice that the console prints the same thing each time, and that the strs[h] is only one character long. When you increment the i to 1, you're trying to access the second element of a one element array.
When the input ["flower","flow","flight"] is put in, it works just fine and get the output "fl". However, when I get to the input ["ab", "a"], I suddenly get an IndexOutOfRangeException. Anyone know why?
Because the algorithm as written loops until i has reached the length of the first string, not the shortest string. This is fine for flower/flow/flight because all these strings will find the common prefix "fl" before i comes close to running off the end of the shortest string; i is 2 by the time the algorithm determines that the o in flower is different to the i in flight and hence the code doesn't go out of bounds.
In the ab/a case, i is 1 and the algorithm hasn't yet determined the prefixes have diverged, you attempt to access the nonexistent index 1 on string "a" and get a crash
As comments have pointed out you also have a problem on your h logic; h should be cycled starting from 1 in a loop of its own inside the i loop. As it is now h just increments up to the number of strings-1 and stays there so in essence you end up only looking for prefixes in the first and last strings. If your strings were flower/flight/float/flowing/flowers you'd declare a prefix of "flower" because flight/float/flowing would only be considered when i was 0, 1 and 2 respectively
I suggest you write out the algorithm in comments, in the language you think in then have a go at turning it into c#
I want lines as many as the width of the console to simultaneously write downwards one char to the height of the console. I've done most of it, but it goes from top to bottom to right etc...
If you need help picturing what I mean, think of the matrix code rain.
int w = Console.WindowWidth;
int h = Console.WindowHeight;
int i = 0;
while (i < w)
{
int j = 0;
while (j < h)
{
Thread.Sleep(1);
Console.SetCursorPosition(i, j);
Console.Write(".");
j++;
}
i++;
}
What I would do is construct a List<string> lines; that would contain the lines you want to write to the console window, where each line is as wide as the console width. Then just print the list out to the console window in reverse order, so the first line (at lines[0]) will always be the last one printed, and will always be at the bottom of the console window.
Sample Implementation -- someone mentioned this might be homework. I did not think so, but if it is, then please try your own implementation of the above idea first.
We can add new items to the list in the same loop that we use to print out its items. Before we add a line, however, we first check to see if there are already as many lines in the list as there are in the console window (Console.WindowHeight). If there are, then we just remove the line at lines[0] before we add a new one. In this way, the List<string> lines is "scrolling" along with the console window.
The scrolling speed is controlled by a Thread.Sleep, but this code could easily be added to a Timer instead, so that other work could happen in the background (like if this was intended to be a "screensaver", and you wanted to wait for user input to "wake up"). But no matter how we decide to implement the speed, I decided to create an enum with values that represent the number of milliseconds a Thread.Sleep implementation would use:
class Program
{
enum MatrixCodeSpeed
{
Fastest = 0,
Faster = 33,
Fast = 67,
Normal = 100,
Slow = 333,
Slower = 667,
Slowest = 1000
}
I would also create a helper method that creates a "random" line for you. It could take in an integer that specifies the "density", which means how many characters you'd want in the line. density represents a percentage, so if 10 is specified, then we pick a random number between 0 and 99, and if it's less than 10 then we add a random matrix character to the string (otherwise we add a space character).
Also, in order to replicate the matrix a little closer, I've also chosen 4 different characters to print, each one slightly darker than the previous. This adds to the three dimensional effect, where the faded blocks look further away than the solid ones:
private static Random rnd = new Random();
// Add whatever 'matrix' characters you want to this array. If you prefer to have one
// character chosen more often than the others, you can write code to favor a specific
// index, or just add more instances of that character to the array below:
private static char[] matrixChars = new[] { '░', '▒', '▓', '█' };
static string GetMatrixLine(int density)
{
var line = new StringBuilder();
for (int i = 0; i < Console.WindowWidth; i++)
{
// Choose a random number from 0-99 and see if it's greater than density
line.Append(rnd.Next(100) > density
? ' ' // If it is, add a space to reduce line density
: matrixChars[rnd.Next(matrixChars.Length)]); // Pick a random character
}
return line.ToString();
}
Next, we have the main method, which populates a list with random lines (using a density of 10%), then prints them out one at a time, in reverse order, in an endless loop (removing the first line if we need to):
static void Main()
{
var lines = new List<string>();
var density = 10; // (10% of each line will be a matrix character)
var speed = MatrixCodeSpeed.Normal;
// Hide the cursor - set this to 'true' again before accepting user input
Console.CursorVisible = false;
Console.ForegroundColor = ConsoleColor.DarkGreen;
while (true)
{
// Once the lines count is greater than the window height,
// remove the first item, so that the list "scrolls" also
if (lines.Count >= Console.WindowHeight)
{
lines.Remove(lines[0]);
}
// Add a new random line to the list, which will be the new topmost line.
lines.Add(GetMatrixLine(density));
Console.SetCursorPosition(0, 0);
// Print the lines out to the console in reverse order so the
// first line is always last, or on the bottom of the window
for (int i = lines.Count - 1; i >= 0; i--)
{
Console.Write(lines[i]);
}
Thread.Sleep(TimeSpan.FromMilliseconds((int)speed));
}
}
}
Here's a gif of it in action, up to the point where the screen is full (then the gif repeats, but the code version continues to scroll normally):
The task smells like an assignment, so I'm guiding you instead feeding the implementation. It is not ethical to feed you with an answer if it is a homework.
You are looking for a better fit of algorithm. The stated algorithm fill the console from top to bottom, as it iterate to fill through the Y-axis first (the nested loop) and followed by the X-axis (the outer loop).
What is needed is to iterate x-axis and y-axis alternatively so that it looks like it fills from the top left corner to the bottom right corner.
// 1 step to (0,0)
*
// 3 steps to (1,1)
**
**
// 5 steps for reaching (2,2)
***
***
***
// 7 steps for reaching (3,3)
****
****
****
// 9 steps for reaching (4,4) and 11 steps for (5,5)...
// I do think everyone could get this pattern
This draft would also be the final outcome of what it looks like.
Instead of filling them all at the same time, what you need is actually get the thread sleep after it reach the next square point.
(Computers are so fast that it probably do all its work to feed your screen within a second and the black console window is gone without any notice.)
At the time you posted the question, I'm also solving it from the very beginning. I thought of filling X and Y axis alternatively is the solution, but stopping at each time that the square expands is far more important to get the effect.
It is not a threading problem tag either at my point of view.
Let's sum up the above pattern:
Assume i and j are x and y coordinates respectively.
Each iteration takes you from (i, j) and n*2+1 steps to reach
(i+1,j+1)
Note that we are zero-based in this example.
We are about to construct the loop:
The n*2+1 step number is useful. It means you need to fill x-axis for
n times and y-axis for n times, and finally get the diagonal grid
(n+1,n+1) done.
In each inner loop, we first render the X frontier along y-axis and
then render the Y frontier along x-axis.
Let say the cycle start with the checkpoint (n,n), where n=3, and we
slept for a while, so we are in n=4 now.
To achieve this, we'd better first navigate to (n+1,0) then fill up
to (n+1,n)
Afterwards we navigate to (0,n+1) and fill to (n+1,n+1)
Then we are in m=n+1 now (sounds like a mathematical proving :(
The loop would be
//calculate how many checkpoints (n)
int checkpoints = 1080;
//n should indicate the actual turn we are instead of naming the total turns like sucks
//The main, the outermost For-loop
for (int n=0;n<checkpoints;n++)
{
// The nested step
for (int y=0;y<n;y++)
{
// Just fill in (n+1, y) grid
Console.SetCursorPosition(n+1, y);
Console.Write(".");
}
for (int x=0;x<n+1;x++)
{
// Just fill in (x, n+1) grid
Console.SetCursorPosition(x, n+1);
Console.Write(".");
}
// Upon completion of each main cycle we have a sleep, yah
Thread.Sleep(100);
}
Well, I expect the program to crash when the console size is smaller than 1080x1080.
This algorithm could only get you a square to fill, and a typical monitor with resolution 1920x1080 just fails as it is 16:9. This is intentional, if you're doing homework you need to configure it before shipping it to your teacher. (I've got no chance to do an assignment as I self learned programming :(
(The site continuously urging me to format my code, this has been half an hour and I just didn't do things wrong. So I decided to post it bit by bit to debug that. Finally I've got the job done...)
If you just want to write one line at a time you can use this:
int w = Console.WindowWidth;
int h = Console.WindowHeight;
int i = 0;
while (i < h)
{
Console.WriteLine(new string('.', w-1));
Thread.Sleep(20);
i++;
}
Just a bit of modification allow the code to simulate the matrix code rain.
int w = Console.WindowWidth;
int h = Console.WindowHeight;
int i = 0;
while (i < h)
{
int j = 0;
string s = "";
Thread.Sleep(10);
while (j < w)
{
Console.SetCursorPosition(j, i);
s += ".";
j++;
}
Console.Write(s);
i++;
}
basically what i did here is just some restructuring of the logic and putting in the proper delays at the right position. Hope it helps.
I am trying to create a text game in C# with console interface
The basic process goes like this:
Take user input.
Manipulate the map (2d array) based on the user input.
Print out the map.
Repeat.
The game works fine, but my problem is that it flickers whenever you try to move the character because it has to go through an entire nested for loop to print out the map each time.
Can I change still different parts of the console output to avoid flickers?
My current actual code for display map at every step:
Console.Clear();
for (int y = 0; y < 15; y++)
{
for (int x = 0; x < 58; x++)
{
// map is an array with current state for each cell on the map
Console.Write(map[y, x]);
}
Console.WriteLine();
}
You should not reprint all the map for each cycle. The better way is to use Console.SetCursorPosition method and rewrite just modified symbols:
foreach(var changedSymbol in changes)
{
Console.SetCursorPosition(changedSymbol.Row, changedSymbol.Column)
Console.Write(changedSymbol.Value);
}
Background -
I am new to programming in C# and am trying to code a custom indicator. On a trading platform that uses C#. A histogram with
positive Y axis = reqAskArraySum
negative Y axis = reqBidArraySum
The inbuilt compiler shows no errors. However the desired results do not seem to show up.
I know/it is possible there are some platform specific initialization problems i.e. code that I have not entered yet correctly.
Question -
The question here is with regards to the code posted below , which is a part of the whole code.
I would like to know whether the posted code satisfies the below objectives.
The objective here is to get a 'number' using a method.
Then only accept selected 'numbers' into an array. The selection/filtration is done by an 'If' statement
Any help and pointers would be highly appreciated.
int i=0;
double iAskSize = GetLevel2Size(ASK,0); //GetLevel2Size(ASK,0) is the method that helps me to retrieve the ASK side 'numbers'//
double iBidSize = GetLevel2Size(BID,0); //GetLevel2Size(BID,0) is the method that helps me to retrieve the BID side 'numbers' //
if(iAskSize>=AskTH_value) //the number should be >= user defined AskTH_value, this is the filtration of the Ask Side 'numbers'//
I am trying to get the filtered iAskSize 'numbers' into the array
reqAskSize, I believe there is a problem here. However I am not sure
{
double[] reqAskSize = new double[1000];
double reqAskArraySum = 0;
for(i=0;i<reqAskSize.Length;i++)
{
reqAskArraySum = reqAskArraySum + reqAskSize[i];
}
SetValue(0,reqAskArraySum);
}
if(iBidSize>=BidTH_value) **//the number should be >= user defined BidTH_value,this is the filtration of the Bid Side 'numbers'//**
I am trying to get the filtered iBidSize 'numbers' into the array
reqBidSize, I believe there is a problem here. However I am not sure
{
double[] reqBidSize = new double[1000];
double reqBidArraySum = 0;
for(i=0;i<reqBidSize.Length;i++)
{
reqBidArraySum = reqBidArraySum + reqBidSize[i];
}
SetValue(1,-reqBidArraySum);
}
If you are trying to add selected numbers into an array, once a number has been selected (through a conditional like if/else), the number should be set in the array.
For example
int[] array = new int[6];
for(int val = 0; val < 6; val++)
{
if(array[val] > 0)
array[val] = 6;
}
Also to obtain a numeral, a return statement makes clear if anything is got.
You should try and see where a return statement may belong within your code.
I've stored a list of colors in my program. I am after an object in my scene to one of the colors in the list. So far, I have done the followings:
if(Input.GetKeyDown(KeyCode.O))
{
for(int i = 0; i < claddingColor.Count; i++)
{
claddingMaterial.color = claddingColor[i];
}
}
This isn't working due to a reason I know (and you can probably spot) but I lack to the verbal fortitude to write it down.
As opposed to have a multiple lines of the following:
claddingMaterial.color = claddingColor[0];
Each tied to different buttons, I like a way I can emulate the above but tie it to a single button press. Thus, if I hit the 0 button 5 times, it will loop through each color stored in the list. If I hit it for a sixth time, it will go back to the first color in the list.
Could someone please help me implement this? Or point me to something that I may learn how to do it for myself?
Define LastColor property as class member:
int LastColor;
In your function use modulo
if(Input.GetKeyDown(KeyCode.O))
{
claddingMaterial.color = claddingColor[(LastColor++) % claddingColor.Count];
}
Note: Depending on the type of claddingColor use Count for a List or Length for Array.
You won't need a for loop
int lastStep = 0;
if(Input.GetKeyDown(KeyCode.O))
{
claddingMaterial.color = claddingColor[lastStep++];
if (lastStep == claddingColor.Count)
lastStep = 0;
}