Array Sorting Issues in C++ - c++

I am trying to make a program that sorts an array without using the sort function (that won't work with objects or structs). I have made the greater than one work, but the less than one keeps changing the greatest element in the array to a one and sorting it wrong, and when used with the greater than function, the first element is turned into a large number. Can someone please help me fix this or is it my compiler.
void min_sort(int array[], const unsigned int size){
for(int k = 0; k < size; k++) {
for(int i = 0; i < size; i++) {
if(array[i] > array[i+1]){
int temp = array[i];
array[i] = array[i+1];
array[i+1] = temp;
}
}
}
}

You are not looping correctly. Looks like you are trying bubble sort which is:
void min_sort(int array[], const unsigned int size){
for(int k = 0; k < size; k++)
for(int i = k+1; i < size; i++)
if(array[i] < array[k]){
int temp = array[i];
array[i] = array[k];
array[k] = temp;
}
}

void min_sort(int array[], const unsigned int size)
{
for(int i=0;i<size-1;i++)
{
for(int j=0;j<size-1-i;j++)
{
if(array[j]>array[j+1])
{
swap(array[j] , array[j+1]);
}
}
}
}
I see that you are trying to implement the bubble sort algorithm. I have posted the code for bubble sort here. In bubble sort you basically compare the element at an index j and the element next to it at index j+1. If array[j] is greater than array[j+1] , you swap them using the swap() function or by using the temp method. The outer loop will run size - 1 times , and the inner loop will run size - 1 - i times because the last element will already be in place.
For Example we have an array of size 4 with elements such as :
array[i] = [100,90,8,10]
The bubble sort will sort it in the following steps :
90,100,8,10
90,8,100,10
90,8,10,100
8,90,10,100
8,10,90,100
8,10,90,100
See, the use of size-1-i . You can see the nested loop runs less number of times in each iteration of the outer loop.

There is only one mistake that your 2nd loop condition should be: i < size -1.
So it should be:
for (int i = 0; i < size -1; i++)

Your attempt at bubble sort is basically correct, you just have an out of bounds issue with your inner loop. During the inner loop's last run, i == size - 1, therefore i + 1 is equal to size, thus data[i+1] is out of range. Simply change the condition of your for to be i < size - 1.
Working example: https://godbolt.org/z/e5ohWPfTz

Related

comparing one array element with the next element to find what is the biggest element

I'm trying to find a way to iterating while comparing the element with the next element to find what is the biggest element in the array. But, the output i want keep repeating as much as the loop run.
int main(){
int array[4];
for ( int i = 0; i < 4; i++){
cin >> array[i];
}
for (int i:array){
for (int j = 1; j < 4; j++){
if (i < array[j]){
break;
}
if (i > array[j] ){
cout << i;
}
}
}
}
You can use the following program to find the biggest element in the array. Note that there is no need to use two for loops as you did in your code snippet.
#include <iostream>
int main()
{
int array[4] = {1,10, 13, 2};
int arraySize = sizeof(array)/sizeof(int);//note that you can also use std::size() with C++17
int startingValue = array[0];
for(int i = 1; i < arraySize; ++i)//start from 1 instead of 0 since we already have array[0]
{
if(array[i] > startingValue)
{
startingValue = array[i];
}
}
//print out the biggest value
std::cout<<"the biggest element in the array is: "<<startingValue<<std::endl;
return 0;
}
Your program is reapeating output because you have the cout inside the if which is satisfied multiple times(depending upon how big the array is and what elements it contains). For example, if you try your example on the array int array[] = {23,2,13,6,52,9,3,78}; then the output of your program will be 2323231313652525293787878 . So the output is reapeating more than 2 times. You can instead use the version i gave that uses only 1 for loop and prints the correct biggest element only once.
Note that you can also use std::size with C++17 while sizeof(array)/sizeof(int) works with all C++ versions.

How to Compare multiple variables at the same time in the C++?

I'm making Sudoku validater program that checks whether solved sudoku is correct or not, In that program i need to compare multiple variables together to check whether they are equal or not...
I have provided a snippet of code, what i have tried, whether every su[][] has different value or not. I'm not getting expecting result...
I want to make sure that all the values in su[][] are unequal.
How can i achieve the same, what are mistakes in my snippet?
Thanks...
for(int i=0 ; i<9 ;++i){ //for checking a entire row
if(!(su[i][0]!=su[i][1]!=su[i][2]!=su[i][3]!=su[i][4]!=su[i][5]!=su[i][6]!=su[i][7]!=su[i][8])){
system("cls");
cout<<"SUDOKU'S SOLUTION IS INCORRECT!!";
exit(0);
}
}
To check for each column uniqueness like that you would have to compare each element to the other ones in a column.
e.g.:
for (int i = 0; i < 9; ++i) {
for (int j = 0; j < 9; ++j) {
for (int k = j + 1; k < 9; ++k) {
if (su[i][j] == su[i][k]) {
system("cls");
cout << "SUDOKU'S SOLUTION IS INCORRECT!!\n";
exit(0);
}
}
}
}
Since there are only 8 elements per row this cubic solution shouldn't give you much overhead.
If you had a higher number N of elements you could initialize an array of size N with 0 and transverse the column. For the i-th element in the column you add 1 to that elements position in the array. Then transverse the array. If there's a position whose value is different from 1, it means you have a duplicated value in the column.
e.g.:
for (int i = 0; i < N; ++i) {
int arr[N] = {0};
for (int j = 0; j < N; ++j)
++arr[su[i][j] - 1];
for (int i = 0; i < N; ++i) {
if (arr[i] != 1) {
system("cls");
cout << "SUDOKU'S SOLUTION IS INCORRECT!!\n";
exit(0);
}
}
}
This approach is way more faster than the first one for high values of N.
The codes above check the uniqueness for each column, you would still have to check for each row.
PS: I have not tested the codes, it may have a bug, but hope you get the idea.

Intersection of 2 dynamically allocated arrays c++

I am trying to create a function that will find the intersection of two dynamically allocated arrays comparing array 1 to array 2. For any values in array 1 that are not in array 2, those values should be deleted in array 1 so that array 1 now only holds the common values of both arrays (no repeats). I cannot use vectors, hashes, or any other thing outside of my current functions in my class:
here is my code so far:
bool IntSet::contains(int val) const
{
for (int i = 0; i < numValues; i++)
{
if (set[i] == val)
return true;
}
return false;
}
this function compares an integer parameter to values currently stored in the array...if a value is in the array it returns true and if else false;
this next function takes in a value and removes that value from the array:
void IntSet::remove(int val)
{
for (int i = 0; i < numValues; i++)
{
if (set[i] == val)
for (int j = 0; j < numValues; j++)
set[j] = set[j + 1];
}
numValues--;
}
here's where I've been having problems, this next function is supposed to iterate through one array and compare those values with the values in the other array...if one value from one array is in the other, it should just skip it, but if a value is not in the array calling the function, it should delete that value from the calling array:
void IntSet::removeDifferent(const IntSet &set2)
{
for (int i = 0; i < set2.size(); i++)
{
if (!set2.contains(set[i]))
{
remove(set[i]);
}
}
}
ive tried about 50 different variations on the removeDifferent() function and I just can't seem to figure this one out. Could someone point me in the right direction?
You're iterating i through the indexes of set2, but then you're testing set[i]. Try this:
void IntSet::removeDifferent(const IntSet &set2)
{
for (int i = 0; i < numValues; ) {
if (!set2.contains(set[i])) {
remove(set[i]);
} else {
i++;
}
}
Note that I also removed i++ from the for loop header. This is because when you remove an element, all the following elements are shifted down, so the next element takes its place in the array. If you incremented i, it would skip that element.
You also need to fix remove. It should start its inner loop from i, so it only shifts down the elements after the one being removed, and it should stop at numValues-1, so it doesn't try to access outside the array when it copies set[j+1]. And as an optimization, it can break out of the outer loop once it has found a match (I assume IntSet doesn't allow duplicates, since you only decrement numValues by 1).
void IntSet::remove(int val)
{
for (int i = 0; i < numValues; i++)
{
if (set[i] == val) {
for (int j = i; j < numValues - 1; j++) {
set[j] = set[j + 1];
}
break;
}
}
numValues--;
}
Your problem is in your remove() function:
void IntSet::remove(int val)
{
for (int i = 0; i < numValues; i++)
{
if (set[i] == val)
for (int j = 0; j < numValues; j++)
set[j] = set[j + 1];
}
numValues--;
}
You can figure out yourself why this is wrong by using a paper and pencil here. Start with a typical example: let's say you found the value you're looking for in the third element of a five-element array:
if (set[i] == val)
In this example, i would be set to 2, and numValues would be set to five. It doesn't matter what val is. Whatever it is, you found it when i is 2, and numValues is five: you found it in the third element of a five element array. Keep that in mind.
Now, you know that you are now supposed to remove the third element in this five element array. But what do you think will happen next:
for (int j = 0; j < numValues; j++)
set[j] = set[j + 1];
Well, using the aforementioned paper and pencil, if you work it out, the following will happen:
set[1] will be copied to set[0]
set[2] will be copied to set[1]
set[3] will be copied to set[2]
set[4] will be copied to set[3]
set[5] will be copied to set[4]
There are two problems here:
A) There is no set[5]. Recall that this is a five-element array, si you only have set[0] through set[4]
B) You're not supposed to copy everything in array down to one element. You have to copy only the elements after the element you want to remove.
Fix these two problems, and you will probably find that everything will work correctly.

c++ array can't get the right array

I have Array A[9]= {1,2,3,4,5,6,7,8,9} and I need to delete the numbers which are not dividing by 2. The code I tried to do:
int main()
{
int n;
ifstream fd(Cdf);
fd>>n; // read how many numbers are in the file.
int A[n];
for(int i = 0; i < n; i++)
{
fd >> A[i]; //read the numbers from file
}
for(int i = 0; i < n; i ++) // moving the numbers.
{
if(A[i] % 2 !=0)
{
for(int j = i; j < n; j++)
{
A[i] = A[i+1];
}
}
}
fd.close();
return 0;
}
But I get numbers like 224466888. what I need to do to get 2,4,6,8?
I need to delete numbers in the same array.
First you should use std::vector for dynamic size arrays.
Second, for removing numbers that are even in a vector, you can do :
std::vector<int> inf = {12,0,5,6,8};
auto func = [](int i){return i % 2 != 0;};
inf.erase(std::remove_if(inf.begin(),inf.end(),func), inf.end());
EDIT :
Ok, so you can still do this without std::vectors, but it will be uglier :
#include <algorithm>
int res[] = {2,5,9,8,6,7};
int size = 6;
auto func = [](int i){return i % 2 != 0;};
int new_size = std::remove_if(res,res + size, func) - res;
All the data you want is in [0, new_size[ range, the other part of your array is now garbage.
Your removal loop is indexing with the wrong variable:
for(int j = i; j < n; j++)
{
A[i] = A[i+1];
}
You're using i, which doesn't change in the loop.
Change it to j. You also need to subtract one from the upper limit, as you'd step outside of the array otherwise when accessing A[j + 1].
for(int j = i; j < n - 1; j++)
{
A[j] = A[j + 1];
}
An array can't be used for your purpose. It is allocated on stack and its size can't be changed dynamically (you can't change the size of an array in general, not only when it is allocated on stack).
You could allocate a second array and keep reallocating it with realloc everytime you add a new element but that's not the good way to do it. You are working with C++ so just use a std::vector<int> and your problems will be solved:
std::vector<int> evenArray;
evenArray.reserve(sizeof(A)/sizeof(A[0])/2);
if (number is even) {
evenArray.pushBack(number);
}
Mind that vector stores elements contiguously so this is legal:
int *evenA = &evenArray[0];
For your inner for loop you should be referencing j, not i.
for(int j = i; j < n - 1; j++)
{
A[j] = A[j+1];
}
Otherwise, what's the point of creating j?
Of course, this also means if you read the whole array back you will display all the characters that were shifted (which will just be equal to the last number). So, you should probably keep track of the new length of the array and just iterate to that instead of the end of the array.
EDIT:
In the inner for loop you need to loop to n - 1 otherwise when you have A[j + 1] it will go off the end of the array when you to change it, which may or may not give you a runtime error.

Insert values from one array to another directly sorted

So what I have to do is insert certain values from one array to another one directly sorted without having to sort them later using BubbleSort or QuickSort or any other method. I can't think of a way to do this... I have to insert them from the biggest value to the smallest one. Here's what I have until now:
void palindroame (int x[100], int y[100]) {
int i=0, j, k=0, aux;
while (x[i]!=0) {
k++; i++;
}
i=0;
for (i=0; i<=k-1; i++) y[i]=0;
for (i=0; i<=k-1; i++) {
if (palindrom(x[i])!=0 && palindrom(x[i+1])!=0)
if (x[i]<x[i+1]) {
aux=x[i+1]; x[i+1]=x[i]; x[i]=aux;
}
} //wrong
for (i=0; i<=k-1; i++) {
if (palindrom(x[i])) y[i]=x[i];
} //wrong
}
Thanks in advance!
The algorithm you need is selection sort, you can use this to sort and copy at the same time.
You can have a look at priority queues:
http://www.cplusplus.com/reference/queue/priority_queue/
Heres an example of a selection sort i have done recently (in which a is a vector)
should give you enough to go on hope it helps, ask questions if u like
for (unsigned int i = 0; i < a.size()-1; i++)
{
int min = i;
for(unsigned int j = i +1; j < a.size(); j++)
{
// If new minimum is found then stores this as the new minimum
if(a[j] < a[min])
{
min = j;
}
}
// Stores the values in the array in ascending order
if (min != i)
{
int temp = a[i];
a[i] = a[min];
a[min] = temp;
}
}
// Returns the array in ascending order
return a;
Edit: just to clarify this is working on a vector that already has values in it in case that wasnt clear but example with code comments i think is enough to help you IMO