i have trying to imlement IntSetArray in c++ it compiles fine but result is wrong first 300 is ok and other numbers are below zero something very strange numbers .e.g -8231313 something like this)
what is wrong? it is code
#include <iostream>
using namespace std;
int quantity=10;
class Set
{
private :
int n,*x;
public:
Set(int maxval){
x=new int[quantity+1];
n=0;
x[0]=maxval;
}
int size(){ return n;}
void insert(int t){
for (int i=0;x[i]<t;i++)
{
if (x[i]==t)
return ;
for (int j=n;j>=i;j--)
x[j+1]=x[j];
x[i]=t;
}
n++;
}
void display()
{
for (int i=0;i<n;i++){
cout<<x[i]<<" "<<"\n";
}
}
};
int main(){
Set s(300);
s.insert(123);
s.insert(45);
s.insert(89);
s.insert(50);
s.insert(13);
s.insert(19);
s.display();
return 0;
}
Think through what happens the first time you try to insert something. x[0] contains 300 and t, what you are trying to insert, is 123.
The first statement in the insert method is this:
for (int i=0;x[i]<t;i++)
This for loop increments i while the ith element of x is less than t. But the 0th element of x is 300, which is not less than 123, so the loop never executes at all. Since in the constructor you only initialized the first element of x, the remainder have garbage values which are never changed.
I think that you most likely don't want the second loop to be inside the first loop anyway. What it seems that you are trying to do with the outer loop is find the first position in x where the value is greater or equal to t, and then the inner loop shifts everything down and inserts t. Then what you should be doing is this:
void insert(int t){
int i; // Declare this outside the first loop so that it
// remains accessible afterwords
for (i=0;x[i]<t;i++)
{
// Do nothing; the whole point is to increment i
}
// Now i contains the first index of x where x[i] >= t
// So now do the shift and insert:
if (x[i]==t)
return ;
for (int j=n;j>=i;j--)
x[j+1]=x[j];
x[i]=t;
n++;
}
A different, and potentially easier to understand, way to write this:
int i;
for (i=0;x[i]<t;i++)
{
// Do nothing; the whole point is to increment i
}
Is this:
int i = 0;
while (x[i] < t) ++i;
Why not use a std::set<int>?
Related
int search( int arr[], int size, int num) {
int i, loc;
loc=i;
for (i=0;i<size;i++){
if (arr[i]==num)
return loc;
else
return -1;
}
}
can someone tell me where did I go wrong?
There are several problems with the shown code as described below.
Problem 1
The variables i and loc are uninitialized and using those uninitialized variables(which you did when you wrote loc = i) is undefined behavior.
Problem 2
The logic that you've used for the for loop and also for the if else part is not correctly implemented. In particular, suppose the for loop is not entered due to the condition i<size being false, then no return statement will be encountered for your non-void returning function again leading to undefined behavior.
Solution
There is no need to create a variable named loc. You can just directly return i when the element is found. Moreover there is no need for the else block. If the element is not found while iterating through the elements, we just return -1 after the for loop.
int search( int arr[], int size, int num) {
for (int i=0; i < size; i++)
{
if (arr[i]==num)
return i;//value found so return i directly
}
return -1; //value was never found
}
int main()
{
int arr[] = {1,2,33,54,3};
std::cout<<search(arr, 5, 3)<<std::endl; //prints 4
std::cout<<search(arr, 5, 33)<<std::endl; //prints 2
std::cout<<search(arr, 5, 98)<<std::endl; //prints -1
}
Working demo.
Here is a solution that resolves the issues in your initial code. Let's break it down by commenting the code.
int search(int arr[], int size, int num) {
// Initialize `location` to a value, this is very important
// In this case, it's okay to initialize to the "not found"
// value and you can simply `return location` at the end of
// this function.
int location = -1;
for (int index = 0; index < size; index++) {
// Check to see if `arr[index] == num`
// If so, we found `num` in `arr` !
// Otherwise, let the loop continue
if (arr[index] == num) {
// Since we found `num` in `arr`, let's store the index
// by updating our location
location = index;
// We found the index we are looking for
// No need to continue the `for` loop
break;
}
// No need for an `else` here, as it was noted in comments that
// returning in the `else` block would exit your loop early
}
// Just return `location`. It either stores `-1` of the index of `num`
return location;
}
Take time to review your solution and compare it to this particular solution. The primary issues with your original code were
You didn't initialize the loc variable nor did you ever update it before returning. This results in Undefined Behavior.
You had an else statement that returned -1 inside your for loop, which resulted in the loop only ever iterating a single time
Note that there are several ways to write this function and I've just shown one approach. Consider how you could write something functionally equivalent using your own approach.
Also note that you could simplify this code to not use a location variable altogether, as in the answer provided by #AnoopRana. I've left the use of the location variable in my example since it seemed to be closer to what you were originally going for. This solution is verbose in an attempt to help you understand more thoroughly what the algorithm is doing.
#include <iostream>
int search(int arr[], int n , int element)
{
int i = 0;
while (i < n)
{
if (arr[i] == element) {
break;
}
i++;
}
if (i < n)
{
return i;
}
else {
return -1;
}
return 0;
}
int main()
{
int arr[] = { 1, 2, 33, 54, 98 };
int n = sizeof(arr)/sizeof(arr[0]);
int element;
std::cout<<"Enter element to search for ";
std::cin>>element;
std::cout<<search(arr,n,element);
}
I have this function that should take a matrix, compare the diagonal elements of the matrix and find the smallest one.
Here it should compare y[0][1] and y[1][0].
#include <iostream>
int Min(int, int [][2]);
using namespace std;
int main() {
int min, y[2][2];
y[0][0]=5;
y[0][1]=4;
y[1][0]=-9;
y[1][1]=0;
min = Min(2, y);
cout<<min;
return 0;
}
int Min(int k, int x[][2]){
int min=x[0][0];
for(int i=0; i<k;i++){
if(x[i][i]<min){
min=x[i][i];
}
}
return min;
}
It always returns 0. Why?
Here it should compare y[0][1] and y[1][0].
Your function goes through the diagonal of the matrix, it hence checks y[0][0] and y[1][1]. They are 5 and 0. The result is zero, which is to be expected.
Here it should compare y[0][1] and y[1][0].
But that's not what you say here:
int min=x[0][0];
or here:
if(x[i][i]<min){
min=x[i][i];
}
Since i cannot be both 0 and 1 at the same time, this accesses x[0][0] and x[1][1].
And for those elements, 0 is the correct minimum.
As a side note, your Min function can only work with matrices of size 2, so the k parameter is unnecessary. Multi-dimensional arrays are annoying like that.
To iterate over all items instead of just [0][0] and [1][1] you need to do:
for(int i=0; i<k; i++)
{
for(int j=0; j<k; j++)
{
if(x[i][j]<min)
{
min=x[i][j];
}
}
}
int Min(int k,const int x[][2])
{
int min=x[0][0];
for(int i=0; i<k;i++)
{
for(int j=0;j<k;j++)
{
if(x[i][j]<min)
{
min=x[i][j];
}
}
}
Earlier it was always showing zero because it had a mess with the column index. Outer for loop iterates k-1 times with first iteration at i=0, and second at i=1 and during both iterations it assigns the same index to both row and column(i.e., x [0][0] and x[1][1]). Perhaps it must assign the index x[0][0], x[0][1], x[1][0], x[1][1]. Earlier, it had only two iterations(the outer for loop) but now it takes four iterations assigning the appropriate index to both column and rows the efficient number of times.
I have t test cases.
Given two numbers x and n, find number of ways x can be expressed as sum of n-th power of unique natural numbers.
The approach is to either select a number or move to the next one.The ans returned is stored in an array since I am using the dp approach.
This is my code
#include<bits/stdc++.h>
using namespace std;
int arr[101];
int func(int x,int n,int ind)
{
if(arr[x]!=-1)
{
return arr[x];
}
if(x==0)
{
return 1;
}
if(ind>=(sqrt(x)+1))
{
return 0;
}
if(x<0)
{
return 0;
}
//you can either take ind or just move to the next one
arr[x]=func(x-pow(ind,n),n,ind+1)+func(x,n,ind+1);
return arr[x];
}
int main()
{
int t;
cin>>t;
while(t)
{
int ans=0;
memset(arr,-1,sizeof(arr));
int x,n;
cin>>x>>n;
int ind=1;
ans=func(x,n,ind);
cout<<"printing the ans\n"<<ans;
t--;
}
return 0;
}
for input
1
10 2
I am getting
printing the ans
-297160607
though the ans is 1
I inserted a simple debug output in func. For the given input "1 10 2" x sometimes gets negative. This causes UB when accessing the array, but does not necessarily crash.
You already check if x is less than 0, but after using x. Move the if(x < 0) up and you are done.
In general to avoid such mistakes you should use stl containers like std::array or std::vector. Though it is not garantued by the c++ standard, many implementations will performe bounds checking on operator[] when compiled in debug mode. Or you can use at() where the standard garantuess bounds checking.
l changed my code but still cant figure out why it wont sort array...bubble sort only moves all elements one place to the right in my program instead of sorting array...l tired bsort and ssort and both do same thing shift elements for 1 position
#include <stdio.h>
#include <stdlib.h>
#include <time.h>
void bsort(int n,int a[])
{
int i,j,k;
for(i=0;i<n-1;i++)
{
for(j=0;j<n-1;j++)
{
if(a[j]>a[j+1]);
{
k=a[j+1];
a[j+1]=a[j];
a[j]=k;
}
}
}
}
int main()
{
int i,j,k,m,n;
srand(time(0));
printf("Unesi broj clanova niza:");
scanf("%d",&n);
int a[n];
printf("Niz za sortiranje je:\n");
for(int i=0;i<n;i++) //Generisanje niza
{
a[i]=rand()%(81);
}
for(int i=0;i<n;i++)
{
printf("%3d",a[i]);
}
bsort(n,a);
printf("\n\nSortirani niz je:\n");
for(i=0;i<n;i++)
{
printf("%3d",a[i]);
}
}
There are several problems with your bubble sort implementation.
First, this line:
if (a[j] > a[j + 1]); {
is incorrect. The semi-colon terminates the conditional. As a result, the following block executes on every iteration of the inner loop and you end up unconditionally swapping a[j] and a[j+1] for every value of j. This means you're performing a nonsensical rearrangement of the array.
Second, you're not dealing correctly with edge cases in the inner loop. When j == 19, you access a[j+1], which is a[20], which is beyond the end of the array. You thus import garbage data into your array.
Lastly, even after correcting the above, your implementation is needlessly inefficient, in that your inner loop goes through the entire array on each iteration of the outer loop, which it doesn't have to. Hint: Try to think about how the initialization or termination condition of the inner loop could depend on i.
Update (after the OP's rewrite): You only addressed the second issue.
int main() {
int a[20];
srand(time(0));
// array values initialization
for (int i = 0; i < 19; i++) {
a[i] = rand() % (81);
}
// array sorting
bsort(a);
// array printing
for (int i = 0; i < 19; i++) {
printf("%3d", a[i]);
}
}
Codeforces problem 160A-http://codeforces.com/problemset/problem/160/A
I am getting either 1 or 2 as the output for all test cases.I think this is because the for loop at the end of the solution is only running either once or twice only.I am not able to identify why is the loop ending after atmost 2 iterations.What is wrong with my solution.
My solution:
#include<iostream>
using namespace std;
int total(int x,int y,int array[100]) //Function to calculate sum of xth to yth term of array.
{
int z=0;
for(int a=x;a<=y;a++)
{
z+=array[a];
}
return z;
}
int main()
{
int n,coin[],sum1,sum2,i,j,a,temp,noofcoins;
cin>>n;
for(i=0;i<n;i++)
cin>>coin[i];
for(i=0;i<n;i++) //Bubble sorting array in descending order.
{
for(j=0;j<n-i-1;j++)
{
if(coin[j]<coin[j+1])
{
temp=coin[j];
coin[j]=coin[j+1];
coin[j+1]=temp;
}
}
}
noofcoins=0;
sum1=0;
sum2=0;
for(i=0;((i<n)&&(sum1<=sum2));i++)
{
sum1+=coin[i];
sum2=total(i+1,n,coin);
++noofcoins;
}
cout<<noofcoins;
}
First, avoid using global variables. This declaration belongs to the main body
int n,coin[100],sum1,sum2,i,j,temp,noofcoins;
Once you correct it you'll notice the variable i used in the function totalis the same as the one used in main. Just initialize it in the for.
for(int i=x;i<y;i++)
Then, the condition in the final for is wrong. It should be:
for(i=0;((i<n)&&(sum1<=sum2));i++)
You have defined i as a global variable.
You use i both in the function total as in main where you use i for the loop where you call total. So after you called total, i has become a different value, and the loop in main will end.
U have declared i as a global variable and then u are using it at two places and then that's certainly causing the problems
1-there's no reason to declare your variables globally, it's better to declare them in your main() function.
2-Your way of bubble sorting seems to be wrong. The correct way is to sort the bubble until there's no swapping required.
bool flag=flase;
while (!flag){
flag=true;
for(i=0;i<n-1;i++){ //Bubble sorting array in descending order.
if (coin[i]<coin[i+1]){
temp=coin[i];
coin[i]=coin[i+1];
coin[i+1]=temp;
flag=false;
}
}
}
3-your way of passing an array to a function is incorrect. Read the part "Arrays as parameters" on this page for the right way.
4-Finally, you might want to use "new" function to create your array. This way it will not be limited to your maximum array size of 100, and also won't waste memory when your array is smaller than 100.
Read here for learning to use "new" function.
following may help:
int twin(std::vector<int> coins)
{
std::sort(coins.begin(), coins.end());
const int total = std::accumulate(coins.begin(), coins.end(), 0);
int left = total;
int right = 0;
for (size_t i = 0; i != coins.size(); ++i)
{
const int value = coins[coins.size() - 1 - i];
left -= value;
right += value;
if (right > left) {
return 1 + i;
}
}
return 0;
}