Merge sort same output C++ - c++

I wrote the below code for merge sort but it's not working, And I am unable to find out problem!
Every time the output becomes same as input, I think that problem may occur due to vector reference.
I think mergeSort is not creating a new vector for sub array. But I am still confused.
input vector: 5, 4, 3, 2, 1
output: 5, 4, 3, 2, 1
Req output: 1, 2, 3, 4, 5
#include <iostream>
#include <vector>
using namespace std;
void merge(vector<int> &la, vector<int> &ra, vector<int> &A) {
int i = 0, j = 0, k = 0;
// overwriting A using its solved sub arrays i.e la, ra
while (i < la.size() && j < ra.size()) {
if (la[i] <= ra[j]) {
A[k] = la[i];
i++;
k++;
} else {
A[k] = ra[j];
j++;
k++;
}
}
// if any subarray left then
while (i < la.size()) {
A[k] = la[i];
k++;
i++;
}
while (j < ra.size()) {
A[k] = ra[j];
k++;
j++;
}
}
mergeSort function:
void mergeSort(vector<int> &A) {
if (A.size() < 2)
return;
int len = A.size();
vector<int> la, ra;
for (int i = 0; i < len / 2; i++)
la.push_back(A[i]);
for (int i = len / 2; i < len; i++)
ra.push_back(A[i]);
// dividing the proble into subproblem
mergeSort(la);
mergeSort(ra);
// merging the solved subproblem
merge(la, ra, A);
}
Driver function:
int main(void) {
int arr[] = { 5, 4, 3, 2, 1 };
vector<int> A(arr, arr + 5);
for (int i = 0; i < A.size(); i++)
cout << A[i] << " ";
cout << endl;
mergeSort(A);
for (int i = 0; i < A.size(); i++)
cout << A[i] << " ";
return 0;
}

The code posted does not seem to have a problem.
Executing it produces the expected output: 1 2 3 4 5, so there is something else going on that could cause your observations: you might be running an executable produced by a previous or at least different version of the code.

Related

switch specific elements between two arrays and have the switched element placed at end of the first array

i'm trying to make it so if i enter the number 3 , the matrix would change to {1,2,4,5,6,7,8,9,10,11,12,0}, i'm not sure if the method of switching the element between two arrays is the best way to do it and i'm trying to do it using pointers
using namespace std;
#include <iomanip>
int main() {
int arr[3][4] = { 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12 }, i, j,c;
int* ptr = &arr[0][0];
int zero[3][4] = { 0,0,0,0,0,0,0,0,0,0,0,0 };
int* zptr = &zero [0][0];
for (int i = 0; i < 3; i++)
{
for (int j = 0; j < 4; j++)
{
cout << setw(8) << arr[i][j] << ' ';
}
cout << endl;
cout << ' ' << endl;
}
for (i = 0; i < 3; i++) {
if (arr[i][0] = i)
{
break;
}
for (int j = 0; j < 4; j++)
cin >> i;
cout << ptr;
}
return 0;
}
you could use easier approach to achieve this using vector in c++ and by finding the index of the input element, consider this example :
int getIndex(vector<int> v, int K) {
auto it = find(v.begin(), v.end(), K);
// calculating the index of K
// note that here i'm supposed the input is valid
int index = it - v.begin();
return index;
}
and you can use the index you get to 1) append in A the element B[index], 2) assign B[index] to A[index] and 3) erase the element A[index].
hope this can be helpful.

I'm trying to write a sorting algorithm in C++ for practice but it doesnt work

when i run it it lists all the integers in the array but then it drops the last three and and loops forever. i cant figure it out, some constructive criticism would be appreciated.
#include <iostream>
#include <unistd.h>
int ary[8] = {3, 7, 8, 1, 3, 45, 19};
int len (sizeof(ary)/sizeof(ary[0]));
int right = 1;
int g;
int g2;
int main()
{
while(right != len)
{
for(int i = 0; i <= len; i++)
std::cout << ", " << ary[i];
std::cout << "\n";
usleep(120000);
for(int i = 0; i <= len; i++)
{
if(ary[i] <= ary[i + 1])
{
right++;
}
else
{
g = ary[i];
g2 = ary[i + 1];
ary[i] = g2;
ary[i + 1] = g;
}
}
}
}
so what you have tried to do here looks something like bubble sort.
i have fixed the bugs in your code, here's a working version:
#include <iostream>
#include <unistd.h>
int ary[8] = {3, 7, 8, 1, 3, 45, 19};
int len (sizeof(ary)/sizeof(ary[0]));
int right = 1;
int g;
int g2;
int main()
{
while(right != len)
{
// the value of the variable 'right' needs to be reset to 1 everytime you loop
right = 1;
for(int i = 0; i < len; i++)
std::cout << ", " << ary[i];
std::cout << "\n";
usleep(120000);
// as arrays in c++ are zero-indexed, the last element is index len - 1
for(int i = 0; i < len - 1; i++)
{
if(ary[i] <= ary[i + 1])
{
right++;
}
else
{
g = ary[i];
g2 = ary[i + 1];
ary[i] = g2;
ary[i + 1] = g;
}
}
}
}
there is one thing that really caught my eyes and is really bad practice : the way you swapped variables
// you only need at most 3 variables to swap
g = ary[i];
ary[i] = ary[i+1];
ary[i+1] = g;
// or you can do built-in:
std::swap(ary[i], ary[i+1]);
even though trying to figure stuff out by yourself is good practice and usually helps, in this case I think you should read some documentation.
for reference, this is what a conventional bubble sort looks like:
#include <iostream>
int a[] = {3, 7, 8, 1, 3, 45, 19};
const int len = sizeof(a) / sizeof(int);
int main () {
for (int i=0; i<len; ++i) {
for (int j=i+1; j<len; ++j) {
if (a[i] > a[j])
std::swap(a[i], a[j]);
}
}
for (int i=0; i<len; ++i)
std::cout << a[i] << ' ';
return 0;
}
thanks for your time and good luck coding (:
it goes forever becuase the for-loop will compare the last item i[8] with i[8 + 1] and i[8 + 1] is null
so to solve this problem
for(int i = 0; i < len - 1; i++)
instead of
for(int i = 0; i <= len; i++)
try this:
#include <iostream>
#include <unistd.h>
int ary[8] = {3, 7, 8, 1, 3, 45, 19};
int len (sizeof(ary)/sizeof(ary[0]));
int Round = 0;
int g;
int g2;
int main()
{
while(Round != len)
{
for(int i = 0; i < len; i++)
std::cout << ", " << ary[i];
std::cout << "\n";
usleep(120000);
for(int i = 0; i < len - 1; i++)
{
if(ary[i] <= ary[i + 1])
{
continue;
}
else
{
g = ary[i];
g2 = ary[i + 1];
ary[i] = g2;
ary[i + 1] = g;
}
}
Round++;
}
}

Maximum Sub-Array Sum C++

Given an array, I am trying to find the maximum sub-array sum. A sub-array is as follows. For example, I get the following array: [9, -7, 5, 3, 91]. Whilst [9, -7, 5] is a sub-array, [9, 5, 3, 91] is not. My code is below:
#include <iostream>
#include <vector>
using namespace std;
int main() {
int arraylen, subarraylen, subarraysum, itervar1, itervar2, itervar3, incrementvar;
cin >> arraylen;
vector<int> mainarray(arraylen);
vector<int> sumarray(arraylen * (arraylen-1) + 1);
for (itervar1 = 0; itervar1 < arraylen; itervar1++) {
cin >> mainarray[itervar1];
}
sumarray[0] = 0;
for (itervar1 = 0; itervar1 < arraylen; itervar1++) {
for (itervar2 = arraylen; itervar2 > 0; itervar2--) {
subarraylen = itervar2-itervar1;
if (subarraylen < 1) {
continue;
}
vector<int> subarray(subarraylen);
incrementvar = 0;
for (itervar3 = itervar1; itervar3 < itervar2; itervar3++) {
subarray[incrementvar] = mainarray[itervar3];
incrementvar++;
}
subarraysum = 0;
for (itervar3 = 0; itervar3 < subarraylen; itervar3++) {
subarraysum += subarray[itervar3];
}
}
}
return 0;
}
For some reason, it doesn't work; just infinitely loops around. Any help would be appreciated.
First, here is a routine to list all the sub arrays:
vector<int> vec{ 9, -7, 5, 3, 91 };
int sz = vec.size();
for(int start = 0; start < sz; start++)
{
for(int end = start; end < sz; end++)
{
for(int j = start; j <= end; j++)
{
cout << vec[j] << ", ";
}
cout << "\n";
}
}
Now you just have to get the total in loop j, add to a vector sum. You don't need to know the size of sum before hand. Use push_back to add total to sum.
Note, the array itself is included as a sub array, you can exclude that array depending on what the definition is.

Custom sorting algorithm c++

I was tinkering with C++ and I was like let's make a sorting algorithm :)
I did something, but it didn't sort the array but instead the array was overwritten with the max number
I don't know where is my mistake because I ran the algorithm on paper (don't ask) and it was correct.
I tried every modification possible.
any help?
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
int mn = 0, mx = 0;
int a[] = { 4, 8, 5, 2, 6, 9, 0, 3, 1, 7 };
for (int i = 0; i < 10; i++)
{
mn = a[i]; mx = a[i];
for (int j = i; j < 10 - i; j++)
{
mn = min(a[j], mn);
mx = max(a[j], mx);
}
swap(a[i], mn);
swap(a[10-1-i], mx);
}
for(int i=0;i<10;i++)
{
cout<<a[i]<<" ";
}
}
You are not swapping array elements, but basically you write the min/max values to the corresponding places within the array. Their old value is simply overwritten. You need to track the positions of the min/max elements and swap accordingly, e.g. swap(a[i], a[min_pos]). Additionally, you could run your outer loop up until the middle of the array is reached as you put two elements into their place on each iteration.
Here's the working code:
#include <iostream>
#include <cstring>
using namespace std;
int main()
{
int mn = 0, mx = 0;
int a[] = { 4, 8, 5, 2, 6, 9, 0, 3, 1, 7 };
for (int i = 0; i < 10 / 2; i++)
{
int min_pos = i, max_pos = i;
for (int j = i; j < 10 - i; j++)
{
if (a[j] < a[min_pos]) {
min_pos = j;
} else if (a[j] > a[max_pos]) {
max_pos = j;
}
}
int min_val = a[min_pos];
int max_val = a[max_pos];
swap(a[i], a[min_pos]);
swap(a[10-1-i], a[max_pos]);
a[i] = min_val;
a[10-1-i] = max_val;
}
for(int i=0;i<10;i++)
{
cout<<a[i]<<" ";
}
}
Note, you need to take care of 'special cases', e.g. when the min_pos and max_pos are at the ends of the interval - they would be swapped twice staying in their original positions.

C++ displaying array elements

Hi when running this small program, I appear to have an output of the memory addresses rather than the values stored inside them: any ideas? thanks.
#include "stdafx.h"
#include <iostream>
using namespace std;
int main()
{
int a[5] = { 1, 3, 5, 7, 9 };
int b[5] = { 2, 4, 6, 8, 10 };
int c[10] = {};
int j, i;
for(j = 0; j < 10; j++)
{
if (a[j] < b[j])
{
c[j] = a[j];
}
else
{
c[j] = b[j];
}
}
for (i= 0; i < 10; i++)
{
cout << c[i];
}
return 0;
}
Your conditions are wrong. a and b both have size 5, but you are iterating upto size 10.