Consider two sets retained in two arrays. Find the union, intersection and difference (relative complement) of the two sets.
I managed to solve the union and the intersection, but the difference is giving me a hard time. Any hints? And if possible, keep it as simple as possible, without functions or more complex aspects, because I'm a beginner and I still have a lot to learn.
Thank you in advance!
#include <iostream>
using namespace std;
int main()
{
int v1[100], v2[100], u[200], intersection[100], d[100];
unsigned int v1_length, v2_length, i, j, OK = 0, union_length;
cout << "Enter the number of elements of the first array:" << " ";
cin >> v1_length;
cout << "Enter the elements of the first array:" << '\n';
for (i = 0; i < v1_length; i++)
cin >> v1[i];
cout << "Enter the number of elements of the second array:" << " ";
cin >> v2_length;
cout << "Enter the elements of the second array:" << '\n';
for (i = 0; i < v2_length; i++)
cin >> v2[i];
//Union
union_length = v1_length;
for (i = 0; i < v1_length; i++)
u[i] = v1[i];
for (i = 0; i < v2_length; i++)
{
int ok = 0;
for (j = 0; !ok && j < v1_length; j++)
if (v1[j] == v2[i])
ok = 1;
if (!ok)
{
u[union_length] = v2[i];
union_length++;
}
}
cout << "The union of the two sets contained in the arrays is: ";
for (i = 0; i < union_length; i++)
cout << u[i] << " ";
cout << '\n';
//Intersection
unsigned int k = 0;
cout << "The intersection of the two sets contained in the arrays is: ";
for (i = 0; i < v1_length; i++)
for (j = 0; j < v2_length; j++)
if (v1[i] == v2[j])
{
intersection[k] = v1[i];
k++;
}
for (i = 0; i < k; i++)
cout << intersection[i] << " ";
cout << '\n';
//Difference
unsigned int l = 0, OK2 = 0;
cout << "The difference of the two sets contained in the arrays is: ";
for (i = 0; i < v1_length; i++)
{
for (j = 0; j < v2_length; j++)
{
if (v1[i] == v2[j])
OK2 = 1;
if (!OK2)
{
d[l] = v1[i];
l++;
}
}
}
for (i = 0; i < l; i++)
cout << d[i] << " ";
cout << '\n';
return 0;
}
It seems that the intersection is the best place to start. You want the items that only in appear in one of the two arrays, right?
So, for the inner loop, you need to compare all the elements. Then, if no match was found, you have the a unique element.
You need to add the curly braces {} to the for loop. I know that curly braces are distracting at times, but over time, you will probably find it safer to almost always include them to avoid confusion.
for (i = 0; i < v1_length; i++)
for (j = 0; j < v2_length; j++) {
if (v1[i] == v2[j]){
break; // this item is not unique
} else if(j == v2_length - 1){
d[l] = v1[i]; // This is the unique one, add it to the answer array
l++;
}
}
for (i = 0; i < l; i++)
cout << intersection[l] << " ";
cout << '\n';
You're on the right track!
You're doing a few things wrong. Here are some fixes you can try:
Only set OK2 to 0 once per inner-loop
Reset OK2 to 0 at the end of the inner-loop
Only do the insertion into d after the inner-loop has completed
As an optimization, consider breaking after you set OK2 to 1, as you know at that point it can never be set to 0 for the current value pointed to by the outer-loop.
Related
I have an array of numbers input by the user, the program then sorts it in ascending order. I just need to find a way to get the factors of each number in the array and have it be printed out
#include "stdafx.h"
#include <iostream>
#include <limits>
#define MAX 200
using namespace std;
int arr[MAX];
int n, i, j, k;
int temp;
int main()
{
//array declaration
int arr[MAX];
int n, i, j;
int temp;
//read total number of elements to read
cout << "Enter total number of numbers to read: ";
cin >> n;
//check bound
if (n<0 || n>MAX)
{
cout << "Input valid range!!!" << endl;
return -1;
}
//read n elements
for (i = 0; i < n; i++)
{
cout << "Enter element [" << i + 1 << "] ";
cin >> arr[i];
cout << endl;
}
//print input elements
cout << "Unsorted Array elements:" << endl;
for (i = 0; i < n; i++)
cout << arr[i] << "\t";
cout << endl;
//sorting - ASCENDING ORDER
for (i = 0; i<n; i++)
{
for (j = i + 1; j < n; j++)
{
if (arr[i]>arr[j])
{
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
//print sorted array elements
cout << endl;
cout << "Sorted (Ascending Order) Array elements:" << endl;
for (i = 0; i < n; i++)
cout << arr[i] << "\t";
cout << endl <<endl;
//trying to find factors
cout << "Factors of " << arr[i] << " are: " << endl;
for (k = 1; k <= arr[i]; ++i)
{
if (arr[i] % k == 0)
cout << k << endl;
}
system ("pause")
return 0;
}
I want it to print each number from the array with
"The factors of (number) are ...'
"The factors of (next number) are ..."
and so on
The final for-loop should be loop with k and you forgot to increment k.
You should also write i-loop:
//trying to find factors
for (i = 0; i < n; i++)
{
cout << "Factors of " << arr[i] << " are: " << endl;
for (k = 1; k <= arr[i]; ++k)
{
if (arr[i] % k == 0)
cout << k << endl;
}
}
In addition, as pointed out by #LocTran, the upper bound of outer loop should be n-1.
Alternatively, you can easily sort arr using std::sort as follows:
std::sort(arr, arr+n);
Then your code would well work for you:
Live Demo
There are some issues with your source code.
1> Sorting problem with for outer loop
//sorting - ASCENDING ORDER
for (i = 0; i < (n-1); i++)
{
for (j = i + 1; j < n; j++)
{
if (arr[i] > arr[j])
{
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
The upper bound of outer loop should be (n-1), not n as following but maybe you're lucky you won't see the problem when n < MAX. In case of n == MAX you will see the problem
//sorting - ASCENDING ORDER
//for (i = 0; i < n; i++)
for (i = 0; i < (n-1); i++)
{
for (j = i + 1; j < n; j++)
{
if (arr[i] > arr[j])
{
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
2> The print functionality for entire array, you should add the outer loop for index of your array, and change the i++ by k++ in your loop as well
//trying to find factors
cout << "Factors of " << arr[i] << " are: " << endl;
for (k = 1; k <= arr[i]; ++i)
{
if (arr[i] % k == 0)
cout << k << endl;
}
should be replaced by
//trying to find factors
for (i = 0; i < n; i++)
{
cout << "Factors of " << arr[i] << " are: " << endl;
//for (k = 1; k <= arr[i]; ++i)
for (k = 1; k <= arr[i]; ++k)
{
if (arr[i] % k == 0)
cout << k << endl;
}
}
Here is my solution based on modified source code
#include <iostream>
#include <limits>
#define MAX 200
using namespace std;
int arr[MAX];
int n, i, j, k;
int temp;
int main()
{
//array declaration
int arr[MAX];
int n, i, j;
int temp;
//read total number of elements to read
cout << "Enter total number of numbers to read: ";
cin >> n;
//check bound
//if (n<0 || n>MAX)
if (n<0 || n>MAX)
{
cout << "Input valid range!!!" << endl;
return -1;
}
//read n elements
for (i = 0; i < n; i++)
{
cout << "Enter element [" << i + 1 << "] ";
cin >> arr[i];
cout << endl;
}
//print input elements
cout << "Unsorted Array elements:" << endl;
for (i = 0; i < n; i++)
cout << arr[i] << "\t";
cout << endl;
//sorting - ASCENDING ORDER
//for (i = 0; i < n; i++)
for (i = 0; i < (n-1); i++)
{
for (j = i + 1; j < n; j++)
{
if (arr[i] > arr[j])
{
temp = arr[i];
arr[i] = arr[j];
arr[j] = temp;
}
}
}
//print sorted array elements
cout << endl;
cout << "Sorted (Ascending Order) Array elements:" << endl;
for (i = 0; i < n; i++)
cout << arr[i] << "\t";
cout << endl << endl;
//trying to find factors
for (i = 0; i < n; i++)
{
cout << "Factors of " << arr[i] << " are: " << endl;
//for (k = 1; k <= arr[i]; ++i)
for (k = 1; k <= arr[i]; ++k)
{
if (arr[i] % k == 0)
cout << k << endl;
}
}
return 0;
}
So I have 2 arrays. Let's say the first one it's called a and the second one b. The first one uses "i" for it's elements and the second one uses "j".
For example we have a[ 1 2 3 4] and b[3 4 5] it should show c[1 2]. In the array c I want to show the elements that are in a and aren't in b.
This is what I've tried, but without succes:
#include <iostream>
using namespace std;
int main(int argc, char const *argv[]) {
int a[50], b[50], c[50], i, j, k, n, m;
cout << "n= "; cin >> n;
//Read arrays
for (i = 0; i < n; i++) {
cout << "a[" << i << "]: "; cin >> a[i];
}
cout << "\nm= "; cin >> m;
for (j = 0; j < m; j++) {
cout << "b[" << j << "]: "; cin >> b[j];
}
//Show the arrays
cout << endl;
cout << "\na[ ";
for (i = 0; i < n; i++) {
cout << a[i] << " ";
}
cout << "]";
cout << endl;
cout << "\nb[ ";
for (j = 0; j < m; j++) {
cout << b[j] << " ";
}
cout << "]";
//Calculate the difference
k = 0; i = 0;
for (j = 0; j < m; j++) {
if (a[i] != b[j])
c[k] = a[i];
k++;
while (j == m && i < n)
i++;
}
//Show the difference array
cout << endl;
cout << "\nc[ ";
for (i = 0; i < k; i++) {
cout << c[i] << " ";
}
cout << "]";
return 0;
}
If the items are sorted, use std::set_difference:
#include <algorithm>
#include <iostream>
#include <iterator>
#include <vector>
int main()
{
int a[] = { 1, 2, 3, 4 };
int b[] = { 3, 4, 5 };
std::vector<int> cv;
std::set_difference(std::begin(a), std::end(a),
std::begin(b), std::end(b),
std::back_inserter(cv));
for (auto& s : cv)
std::cout << s << "\n";
}
Output:
1
2
The advantage of using the STL algorithms is that the purpose of the code is known immediately just by looking at the name of the function, and that they work every time (if you give them the correct parameters). Note the lack of comments -- any competent C++ programmer understands right away what's being done.
On the other hand, if you didn't mention what your original code was trying to do (including removing the comments), it would take much more effort to figure out what it's supposed to be doing, and as you've seen, it contains bugs.
Your logic is wrong.
Explanation
So the thing that we will do
For each element in a we will have to check if it is there in array b or not.
If we see any element of a[i] in b[1..m] then we can't add it to c.
So in code we just mark it by f=1
When I get out of that second for loop I want to check if that a[i] is eqaul to any of the element in b[1..m] in which case f will be 1. But if it is 0 then add it to array c[].
Correct one
int k=0;
for(int i=0;i<n;i++)
{
int f=0;
for(int j=0;j<m;j++)
if(a[i]==b[j])
f=1;
if(!f)
c[k++]=a[i];
}
Where OP went wrong?
Being not equal to one element of b[] doesn't guarantee that the element is not appearing b[0..m-1] . This is where op went wrong.
In the for loop
for(j=0;j<m;j++) you are checking if particular a[i] is equal to b[j] or not. If that is the case then it is added to c[] . It is wrong. Also i is not incremented in the loop unless j==m and as in the for loop the condition is j<m so i is never incremented. And k is incremented every time so not every element in c is valid they may contain garbage value even after processing.
k = 0; i = 0;
for (j = 0; j < m; j++) {
if (a[i] != b[j]) // this doesn't mean that it is not appearing in `b`
c[k] = a[i];
k++; // k is incremented in every iteration which is wrong. It should be only when we are sure that `a[i]` is not in `b[0..m-1] `
while (j == m && i < n)
i++; // OP is not using it anywhere...this is redundant.
}
what op did?
Compared first element of a[0] with every element of b[0..m-1] and array c[] contains m elements irrespective of what a[] and b[] is, out of which
c[i]={ a[0] if b[j]==a[0]
{ garbage value if b[j] not equal to a[0]
Dry Run of OP's code
k = 0; i = 0;
for (j = 0; j < m; j++) {
if (a[i] != b[j])
c[k] = a[i];
k++;
while (j == m && i < n)
i++;
}
Input
Case: 1 2 3 4 :a[]
2 3 4 1 :b[]
Step 1: i=0 a[0]!=b[0] is true so c[0]=a[0]. the `while loop` not entered.
j++
Step-2: i is still 0. a[0]!=b[1] so it is added c[1]=a[0]. While loop not entered.
j++
Step-3: i is still 0. a[0]!=b[2]. So c[2]=a[0]. While loop skipped.
j++
Step-4: i is still 0. a[0]==b[3] is true so no assignment done. But k is incremented. so c[3]=garbage. j=3 so while loop skipped
j++
Out of for loop.
Output: [here x is garbage value]
a[]: 1 2 3 4
b[]: 2 3 4 1
c[]: 1 2 3 x
Example test case
1 2 3 4 :=a
2 3 4 1 :=b
Corrected Code
#include <iostream>
using namespace std;
int main(int argc, char const *argv[]) {
int a[50], b[50], c[50], i, j, k, n, m;
cout << "n= "; cin >> n;
//Read arrays
for (i = 0; i < n; i++) {
cout << "a[" << i << "]: "; cin >> a[i];
}
cout << "\nm= "; cin >> m;
for (j = 0; j < m; j++) {
cout << "b[" << j << "]: "; cin >> b[j];
}
//Show the arrays
cout << endl;
cout << "\na[ ";
for (i = 0; i < n; i++) {
cout << a[i] << " ";
}
cout << "]";
cout << endl;
cout << "\nb[ ";
for (j = 0; j < m; j++) {
cout << b[j] << " ";
}
cout << "]";
//Calculate the difference
k = 0; i = 0;
int k=0;
for(int i=0;i<n;i++)
{
int f=0;
for(int j=0;j<m;j++)
{
if(a[i]==b[j])
f=1;
if(!f)
c[k++]=a[i];
}
}
//Show the difference array
cout << endl;
cout << "\nc[ ";
for (i = 0; i < k; i++) {
cout << c[i] << " ";
}
cout << "]";
return 0;
}
Your code seems to check if the elements in a are equal to all elements of b. If you just want to check the elements in a if they are equal to at least one element of b, you can do
for (int i=0; i<n; i++) {
bool found = false;
for (int j=0; j<m; j++) {
if (a[i] == b[j]) {
found = true;
break;
}
}
if (!found) {
std::cout << "a["<<i<<"] is not in b"<<std::endl;
}
}
Or add the element to c, but I would recommend to use std::vector<int> c for that.
In the array c I want to show the elements that are in a and aren't in b
It seems like you are looking for std::set_difference
int a[4] = {1, 2, 3, 4}, b[3] = {3, 4, 5};
int c[2] = {}; // declare c with enough space to hold all the elements in result
std::set_difference(a, a + 4, b, b + 3, c); // now c contains the element that are in a but not in b
You can do this very easily using 'set'.
#include<iostream>
#include<set>
int main(){
std::set<int> a = {1,2,3,4} , b = {3,4,5};
for(int const inB : b)
a.erase(inB);
for(int const inA : a)
std::cout << inA << " ";
std::cout << std::endl;
return 0;
}
So, I am trying to implement this algorithm from our textbook.
I wrote this :
// Knapsack_memoryfunc.cpp : Defines the entry point for the console application.
//Solving Knapsack problem using dynamic programmig and Memory function
#include "stdafx.h"
#include "iostream"
#include "iomanip"
using namespace std;
int table[20][20] = { 0 };
int value, n, wt[20], val[20], max_wt;
// ---CONCERNED FUNCTION-----
int MNSack(int i, int j)
{
value = 0;
if (table[i][j] < 0)
if (j < wt[i])
value = MNSack(i - 1, j);
else
value = fmax(MNSack(i - 1, j), val[i] + MNSack(i - 1, j - wt[i]));
table[i][j] = value;
return table[i][j];
}
// --------------------------
void items_picked(int n, int max_wt)
{
cout << "\n Items picked : " << endl;
while (n > 0)
{
if (table[n][max_wt] == table[n - 1][max_wt]) // if value doesnot change in table column-wise, item isn't selected
n--; // n-- goes to next item
else // if it changes, it is selected
{
cout << " Item " << n << endl;
max_wt -= wt[n]; // removing weight from total available (max_wt)
n--; // next item
}
}
}
int main()
{
cout << " Enter the number of items : ";
cin >> n;
cout << " Enter the Maximum weight : ";
cin >> max_wt;
cout << endl;
for (int i = 1; i <= n; i++)
{
cout << " Enter weight and value of item " << i << " : ";
cin >> wt[i] >> val[i];
}
for (int i = 0; i <= n; i++)
for (int j = 0; j <= max_wt; j++)
table[i][j] = 0;
for (int i = 1; i <= n; i++)
for (int j = 1; j <= max_wt; j++)
table[i][j] = -1;
cout << " Optimum value : " << MNSack(n, max_wt);
cout << " \n Table : \n";
for (int i = 0; i <= n; i++)
{
for (int j = 0; j <= max_wt; j++)
if (table[i][j] == -1)
cout << setw(5) << "-";
else
cout << setw(5) << table[i][j];
cout << endl;
}
items_picked(n, max_wt);
return 0;
}
Here is the question and output :
It seems like its correct on some places like optimum value, yet isn't fully acceptable.
I've tried to debug it, but its quite hard with recursive functions. Can someone please help?
int MNSack(int i, int j)
{
value = 0;
if (table[i][j] < 0)
{
if (j < wt[i])
value = MNSack(i - 1, j);
else
value = max(MNSack(i - 1, j), val[i] + MNSack(i - 1, j - wt[i]));
table[i][j] = value;
}
return table[i][j];
}
The problem comes in here. When your table item is greater or equal to 0, you will skip the recursion but still set the table item to 0, which won't be right if your table item is greater than 0.
You only need to update the table item when it needs to be change, so put it in the braces will correct this.
The bottom up solution.
#include <iostream>
#include <algorithm>
#include <iomanip>
using namespace std;
int main()
{
int table[20][20] = { 0 };
int value, n, wt[20], val[20], max_wt;
cout << " Enter the number of items : ";
cin >> n;
cout << " Enter the Maximum weight : ";
cin >> max_wt;
cout << endl;
for (int i = 1; i <= n; i++)
{
cout << " Enter weight and value of item " << i << " : ";
cin >> wt[i] >> val[i];
}
// Initialization
for (int i = 0; i <= n; i++)
for (int j = 0; j <= max_wt; j++)
table[i][j] = 0;
// In practice, this can be skipped in a bottom up solution
for (int i = 1; i <= n; i++)
for (int j = 1; j <= max_wt; j++)
table[i][j] = -1;
for (int i = 1; i <= n; i++)
{
for (int j = 1; j <= max_wt; j++)
{
if (j < wt[i])
table[i][j] = table[i - 1][j];
else
table[i][j] = max(table[i - 1][j], val[i] + table[i - 1][j - wt[i]]);
}
}
cout << " Optimum value : " << table[n][max_wt] << endl;
cout << " \n Table : \n";
for (int i = 0; i <= n; i++)
{
for (int j = 0; j <= max_wt; j++)
if (table[i][j] == -1)
cout << setw(5) << "-";
else
cout << setw(5) << table[i][j];
cout << endl;
}
return 0;
}
You can see that this changes the recursion to a loop, and therefore avoids the global variables. It also makes the code simpler, so that you can avoid checking if the table item is valid (equal to -1 in your example).
The drawback of this solution is, it always traverses all the possible nodes. But it gains better coefficient per item because the recursion and double checking the table item costs more. Both top-down and bottom-up have the same order of complexity O(n^2), and it's hard to tell which one is faster.
I need to write a program that receives 2 arrays and checks how many times 1 is included in the other...
But I cant find what is wrong with my program! tx!!
#include <iostream>
using namespace std;
int main()
{
int vector1[500];
int vector2[100];
int a = 0, b = 0, count = 0, k = 0;
cout << "enter size of first array:" << endl;
cin >> a;
cout << " enter first array values:" << endl;
for (int i = 0; i < a; i++)
cin >> vector1[i];
cout << "enter size of second array:" << endl;
cin >> b;
cout << "enter secound array values:" << endl;
for (int i = 0; i < b; i++)
cin >> vector2[i];
for (int i = 0; i < b; i++)
for (int j = 0; j < a; j++)
if (vector2[i + k] == vector1[j])
{
count++;
k++;
}
else
k = 0;
cout << count << endl;
system("pause");
return 0;
}
Why at all do you need k? The problem is about all inclusions of all elements right? If O(n^2) complexity is fine, then...
for (int i = 0; i < b; i++)
for (int j = 0; j < a; j++)
if (vector2[i] == vector1[j])
count++;
One obvious disadvantage of the code above is that you'll get the total sum of all occurences of elements from vector1 in vector2. The key idea remains the same in case you need to know, which elements exactly appeared in another array and how many times, you'll just have to use map or other vector.
So I'm trying to make a program that will separate one array of ints into two, one for even ints, and one for uneven ints. Now, the strange thing is, if I only enter even or uneven numbers into the base array, the program works fine, but if I enter a mix of the two, one of the values held by the two new array will be a random, usually negative, big number, any idea why that is?
#include <iostream>
using namespace std;
void main()
{
int *a, n, *even_nums = 0, *uneven_nums = 0, counter_even = 0,counter_uneven = 0;
cout << "How many values does your array have?\n" << endl;
cin >> n;
a = new int[n];
cout << "\nEnter the values in your array:" << endl;
for (int i = 0; i < n; i++)
{
cout << "a[" << i << "] = ";
cin >> a[i];
if (a[i] % 2 == 0)
counter_even++;
else
counter_uneven++;
}
if (counter_even == 0)
cout << "There are no even numbers in your array." << endl;
else
even_nums = new int[counter_even];
if (counter_uneven == 0)
cout << "There are no uneven numbers in your array." << endl;
else
uneven_nums = new int[counter_uneven];
for (int i = 0; i < n; i++)
{
if (a[i] % 2 == 0)
even_nums[i] = a[i];
else
uneven_nums[i] = a[i];
}
if (counter_even != 0)
{
cout << "\nThe even numbers in your array are:" << endl;
for (int i = 0; i < counter_even; i++)
cout << even_nums[i] << " ";
}
if (counter_uneven != 0)
{
cout << "\nThe uneven numbers in your array are:" << endl;
for (int i = 0; i < counter_uneven; i++)
cout << uneven_nums[i] << " ";
}
system("PAUSE");
}
In
for (int i = 0; i < n; i++)
{
if (a[i] % 2 == 0)
even_nums[i] = a[i];
else
uneven_nums[i] = a[i];
}
You are using the same index for all of the arrays. This will not work as even_nums and uneven_nums will be smaller than a if you have both. You will eventually be writing past the end of the array which is undefined behavior.
What you need to do is add one index for each array and every time you insert an element into the array then you advance that index.
for (int i = 0, u = 0, e = 0; i < n; i++)
{
if (a[i] % 2 == 0)
even_nums[e++] = a[i];
else
uneven_nums[u++] = a[i];
}
Also you are using void main() which is not standard and should not be used. int main() and int main(int argc, char** argv) are the standard acceptable signatures of main()
In the block
for (int i = 0; i < n; i++)
{
if (a[i] % 2 == 0)
even_nums[i] = a[i];
else
uneven_nums[i] = a[i];
}
you are using i as the same index for arrays a, even_nums and uneven_nums. You need to use separate indexes for these arrays.
For example, if you have n=10 elements, 5 even and 5 odd, your even_nums and uneven_nums contains only 5 elements each.