I am trying to find the number of distinct numbers from input which are not equal to 0. n is in 1-100 range. The numbers in the array are in the 0-600 range.
http://codeforces.com/problemset/problem/937/A
For this question, I wrote a code:
#include <stdio.h>
#include <string.h>
int main(void)
{
int n, count = 0, i;
scanf("%d", &n);
int ar[n], ar2[601];
memset(ar2, 0, 600 * sizeof(int));
for (i = 0; i < n; i++) {
scanf("%d ", &ar[i]);
if (ar2[ar[i]] == 0)
ar2[ar[i]] = 1;
}
for (i = 1; i < 601; i++) {
if (ar2[i] != 0)
count++;
}
printf("%d",count);
return 0;
}
for the first test case (4 1 3 3 2) , it outputs the right answer 3 in ideone.com 's gcc 6.3, but outputs 4 in gcc 5.1 which is used at codeforces.
Why does this happen, and how can I prevent this ?
(I think it's because of memset, but I'm not sure.)
You are defining an array of size n before the value of n has beed determined (note that you scanf the value of n later). This is undefined behaviour, such that different compilers may give different results, and even starting your program on your machine may give different results (including crashes).
instead of
int n, count = 0, i;
int ar[n];
...
write
int n, count = 0, i;
scanf("%d", &n);
int ar[n], ar2[601] = { 0 };
At least the malformed array should then be solved, and ar2 is completely initialized with 0. You can get rid of your memset, which initialized only 600 items (instead of 601) anyway.
Here is a quicker solution to the problem
#include <stdio.h>
int main()
{
bool seen_number_before[601] = { false };
int count = 0;
seen_number_before[0] = true;
int n;
scanf("%d", &n); // Should do error checking here
for (int i = 0; i < n; ++i) {
int v;
scanf("%d", v); // More error checking
if (!seen_number_before[v]) // Not seen it before
seen_number_before[v] = true; // Mark it as seen
++count; // Add to the count
}
}
printf("%d\n", count);
return 0;
}
}
There are some errors in your code, from a[n] when n is not defined.
To check errors try compiling with some useful options:
gcc -Wall code.c -o code -g
the -Wall is for Warning all and the -g is used for debug on valgrind (useful tool to check memory leak and other errors).
Also I suggest you to name properly every var in your code, could helpful for a large size of code base.
This is my solution,
#include <stdio.h>
#include <stdlib.h>
int main(){
int n, count = 0;
scanf("%d", &n);
int *a = malloc(n * sizeof(int));
int hash[600] = { 0 };
for(int i=0; i<n; i++){
scanf("%d ", &a[i]);
if(a[i] != 0){
hash[a[i]] = 1;
}
}
for(int i=0; i<600; i++){
printf("%d ", hash[i]);
if(hash[i] == 1) ++count;
}
printf("\n\n%d\n", count);
return 0;
}
it can be optimized in time, using only one for, and/or in memory by creating an hashset of int, and every int can store 32 bit and do some bitwise operations, so if the nth bit is 1, count++, otherwise don't do nothing.
Related
"I am trying to find the size of the 'list[34]' array but it is being set by random numbers when the program is being initialised. I cannot remove the rand() function in main because that is part of the question and is just added back in by the solution checker when I submit.
I have tried setting all the values in the array to '0' but that throws out the 'list_size' variable if the list is shorter than 35 values since the list is just filled with whatever is parsed into it followed by '0' in all other values.
#include <stdlib.h>
#include <float.h>
// Declare Global variables here.
double list[34];
int list_size;
void array_stats() {
// Insert your solution here.
for(int i = 0; i <= 35; i++)
{
scanf("%lf", &list[i]);
list_size = i;
if (list[i] == 0)
{
break;
}
}
}
#include <stdlib.h>
#include <time.h>
int main() {
// Simulate the test setup process.
srand( time( NULL ) );
for ( int i = 0; i < 34; i++ ) {
list[i] = rand();
}
list_size = rand();
// Call submitted code.
array_stats();
// Display contents of array list.
for (int i = 0; i < list_size; i++) {
printf("%f ", list[i]);
}
printf("\n");
printf("Item count: %d\n", list_size);
return 0;
}```
Expected result for an empty string (echo '' | file_name) is 0
Actual result for an empty string (echo '' | file_name) is 34
If you you whould have used int datatype in your array:
memset(arr, 0, sizeof(arr));
But since your are not, it get's a bit tricky and to clear a double array the best way is:
double list[34];
for (size_t i = 0; i < list; ++i)
arr[i] = 0.0;
Theoretically, you should be safe using memset for floats and doubles, but see the caveats in the answers at Is it legal to use memset(,0,) on array of doubles? in case you have a non-standard floating point implementation.
I am trying to implement Insertion sort algorithm in C.
But all I get is SIGSEGV error in online IDEs and the output doesn't show up in Code::Blocks. How to avoid Such errors.
#include <stdio.h>
#include <stdlib.h>
int main()
{
/* Here i and j are for loop counters, temp for swapping
count for total number of elements,array for elements*/
int i, j, temp, count;
printf("How many numbers are you going to enter");
scanf("%d", &count);
int n[20];
printf("Enter %d elements", count);
// storing elements in the array
for(i = 0; i < count; i++) {
scanf("%d", n[i]);
}
// Implementation of insertion sort algorithm
for(i = 0; i < count; i++) {
temp = n[i];
j = i - 1;
while(temp < n[j]) {
n[j+1] = n[j];
j = j - 1;
}
n[j+1] = temp;
}
printf("Order of sorted elements");
for(i = 0; i < count; i++) {
printf("%d", n[i]);
}
return 0;
}
There are a couple of problems with your code. First of all, what is a SIGSEGV error? Well, it's another name for the good old Segmentation fault error, which is basically the error you get when accessing invalid memory (that is, memory you are not allowed to access).
tl;dr: change scanf("%d",n[i]); to scanf("%d",&n[i]);. You're trying to read the initial values with scanf("%d",n[i]);, this raises a segmentation fault error because scanf expects addresses in which put the values read, but what you're really doing is passing the value of n[i] as if it were an address (which it's not, because, as you did not set any value for it yet, it's pretty much just memory garbage). More on that here.
tl;dr: change int n[20]; to int n[count]. Your array declaration int n[20]; is going to store at most 20 integers, what happens if someone wants to insert 21 or more values? Your program reserved a certain stack (memory) space, if you exceed that space, then you're going to stumble upon another program's space and the police (kernel) will arrest you (segmentation fault). Hint: try inserting 21 and then 100 values and see what happens.
tl;dr: change for(i = 0; i < count; i++) { to for(i = 1; i <= count; i++) {. This one is a logic problem with your indexes, you are starting at i = 0 and going until i = count - 1 which would be correct in most array iteration cases, but as j assumes values of indexes before i, you need i to start from 1 (so j is 0, otherwise j = -1 in the first iteration (not a valid index)).
My final code is as follows. Hope it helped, happy coding!
#include <stdio.h>
#include <stdlib.h>
int main() {
/*Here i and j are for loop counters,temp for swapping
count for total number of elements,array for elements*/
int i, j, temp, count;
printf("How many numbers are you going to enter?\n");
scanf("%d",&count);
int n[count];
printf("Enter %d elements\n",count);
//storing elements in the array
for(i = 0; i < count; i++) {
scanf("%d", &n[i]);
}
//Implementation of insertion sort algorithm
for(i = 1; i <= count; i++) {
temp = n[i];
j = i-1;
while(temp < n[j]) {
n[j+1] = n[j];
j--;
}
n[j+1] = temp;
}
printf("Order of sorted elements\n");
for(i = 0; i < count; i++) {
printf("%d\n",n[i]);
}
return 0;
}
Edit: If you're having trouble with online IDEs, consider running your programs locally, it saves a lot of time, plus: you never know what kernel version or magic the online IDEs are using to run your code (trust me, when you're coding in C -- fairly low level language, these things make a difference sometimes). I like to go all root style using Vim as text editor and gcc for compiling as well as gdb for debugging.
I am trying to make a program that calculates the amount of prime numbers that don't exceed an integer using the sieve of Eratosthenes. While my program works fine (and fast) for small numbers, after a certain number (46337) I get a "command terminated by signal 11" error, which I suppose has to do with array size. I tried to use malloc() but I didn't get it quite right. What shall I do for big numbers (up to 5billion)?
#include <stdio.h>
#include<stdlib.h>
int main(){
signed long int x,i, j, prime = 0;
scanf("%ld", &x);
int num[x];
for(i=2; i<=x;i++){
num[i]=1;
}
for(i=2; i<=x;i++){
if(num[i] == 1){
for(j=i*i; j<=x; j = j + i){
num[j] = 0;
}
//printf("num[%d]\n", i);
prime++;
}
}
printf("%ld", prime);
return 0;
}
Your array
int num[x];
is on the stack, where only small arrays can be accommodated. For large array size you'll have to allocate memory. You can save on memory bloat by using char type, because you only need a status.
char *num = malloc(x+1); // allow for indexing by [x]
if(num == NULL) {
// deal with allocation error
}
//... the sieve code
free(num);
I suggest also, you must check that i*i does not break the int limit by using
if(num[i] == 1){
if (x / i >= i){ // make sure i*i won't break
for(j=i*i; j<=x; j = j + i){
num[j] = 0;
}
}
}
Lastly, you want to go to 5 billion, which is outside the range of uint32_t (which unsigned long int is on my system) at 4.2 billion. If that will satisfy you, change the int definitions to unsigned, watching out that your loop controls don't wrap, that is, use unsigned x = UINT_MAX - 1;
If you don't have 5Gb memory available, use bit status as suggest by #BoPersson.
The following code checks for errors, tested with values up to 5000000000, properly outputs the final count of number of primes, uses malloc so as to avoid overrunning the available stack space.
#include <stdio.h>
#include <stdlib.h>
int main()
{
unsigned long int x,i, j;
unsigned prime = 0;
scanf("%lu", &x);
char *num = malloc( x);
if( NULL == num)
{
perror( "malloc failed");
exit(EXIT_FAILURE);
}
for(i=0; i<x;i++)
{
num[i]=1;
}
for(i=2; i<x;i++)
{
if(num[i] == 1)
{
for(j=i*i; j<x; j = j + i)
{
num[j] = 0;
}
//printf("num[%lu]\n", i);
prime++;
}
}
printf("%u\n", prime);
return 0;
}
problem in Light OJ:
1001 - Opposite Task:
This problem gives you a flavor the concept of special judge. That means the judge is smart enough to verify your code even though it may print different results. In this problem you are asked to find the opposite task of the previous problem.
To be specific, I have two computers where I stored my problems. Now I know the total number of problems is n. And there are no duplicate problems and there can be at most 10 problems in each computer. You have to find the number of problems in each of the computers.
Since there can be multiple solutions. Any valid solution will do.
Input:
Input starts with an integer T (≤ 25), denoting the number of test cases.
Each case starts with a line containing an integer n (0 ≤ n ≤ 20) denoting the total number of problems.
Output:
For each case, print the number of problems stored in each computer in a single line. A single space should separate the non-negative integers.
Sample Input
Output for
Sample Input:
3
10
7
7
Sample output:
0(space)10
0(space)7
1(space)6
my code :
#include<stdio.h>
#include <stdlib.h>
int main()
{
int c,sum;
int i,j,mini=0,maxi;
int com1,com2;
do{
scanf("%d",&c);
}while (c>25);
int t[c+1];
for(i=1; i<=c; i++)
{
do{
scanf("%d",&t[i]);
}while (t[i]>20);
}
for(i=1; i<=c; i++)
{
maxi=t[i];
com1=rand() % (maxi - mini + 1) + mini;
com2=t[i]-com1;
printf("%d %d\n",com1,com2);
}
return 0;
}
When I submit my code the judge gives wrong answer.
But while I compile the code in CodeBlocks it gives right answer.
I can't understand the problem in online judge.
How can I solve it.
The original post has mini=0 for all cases, but where the total problems is > 10 that may not work. I have adjusted that
#include<stdio.h>
#include <stdlib.h>
int main()
{
int c = 0, mini, maxi, i, com1, com2, *t;
scanf ("%d",&c);
t = malloc (c * sizeof(int));
for (i=0; i<c; i++)
scanf ("%d", &t[i]);
printf("\n");
for (i=0; i<c; i++) {
if (t[i]>10) {
maxi = 10;
mini = t[i] - 10;
} else {
maxi = t[i];
mini = 0;
}
com1 = rand() % (maxi - mini + 1) + mini;
com2 = t[i] - com1;
printf("%d %d\n",com1,com2);
}
free (t);
return 0;
}
Please note that results of malloc() and scanf() have not been checked: they should be.
You seem to be looping unnecessary number of times for the input. I have removed the unnecessary loops from your code while retaining the logic you used. I made a silly mistake with my earlier answer.
#include<stdio.h>
#include <stdlib.h>
int main()
{
int c = 0;
int maxi=10;
scanf("%d",&c);
int t[c];
for(int i=0; i<c; i++)
scanf("%d",&t[i]);
for(int i=0; i<c; i++)
{
int com1 = t[i],com2 = 0;
if (t[i] > 10)
{
com1 = 10
com2 = t[i]-com1;
}
printf("%d %d\n",com1,com2);
}
return 0;
}
So all I'm trying to do is take an input from the user of how many cards to use and then randomly assign each card to a different index in an array. I'm having extensive issues getting the rand function to work properly. I've done enough reading to find multiple different ways of shuffling elements in an array to find this one to be the easiest in regards to avoiding duplicates. I'm using GCC and after I input the amount of cards I never get the values from the array back and if I do they're all obscenely large numbers. Any help would be appreciated.
#include <time.h>
#include <stdlib.h>
#include <stdio.h>
void main(){
srand(time(NULL));
int d, c, i, z, l, r;
printf("Enter the deck length: ");
scanf("%d\n ", &c);
int deck[c];
int swap[c];
z = c;
for(l=0; l<c; l++){
swap[l] = l;
}
for(i=z; i=0; i--){
r = rand() / i
deck[i] = swap[r];
for(r; r=(c-1); r++){
swap[r] = swap[(r+1)];
}
}
for(d = 0; d < c; d++){
printf("%d ", deck[d]);
}
return;
}
I can spot one major problem here:
for(i=z; i=0; i--)
^^^
This loop will never execute since you are using assignment(=) and setting i to 0 therefore the condition will always be false, although using equality(==) will still be false in this case, you probably want:
for(i=z; i!=0; i--)
This means you will be using deck unitialized which is undefined behavior. Once you fix that you have a similar problems here:
for(r; r=(c-1); r++){
main has to return int and your return at the end needs to provide a value.
Turning on warning should have allowed you to find most of these issues, for example using -Wall with gcc gives me the following warning for both for loops:
warning: suggest parentheses around assignment used as truth value [-Wparentheses]
Note, see How can I get random integers in a certain range? for guidelines on how to use rand properly.
You basically need to be able to generate 52 numbers pseudo-randomly, without repeating. Here is a way to do that...
First, loop a random number generator 52 times, with a method to ensure none of the random numbers repeat. Two functions in addition to the main() will help to do this:
#include <ansi_c.h>
int NotUsedRecently (int number);
int randomGenerator(int min, int max);
int main(void)
{
int i;
for(i=0;i<52;i++)
{
printf("Card %d :%d\n",i+1, randomGenerator(1, 52));
}
getchar();
return 0;
}
int randomGenerator(int min, int max)
{
int random=0, trying=0;
trying = 1;
while(trying)
{
srand(clock());
random = (rand()/32767.0)*(max+1);
((random >= min)&&(NotUsedRecently(random))) ? (trying = 0) : (trying = 1);
}
return random;
}
int NotUsedRecently (int number)
{
static int recent[1000];//make sure this index is at least > the number of values in array you are trying to fill
int i,j;
int notUsed = 1;
for(i=0;i<(sizeof(recent)/sizeof(recent[0]));i++) (number != recent[i]) ? (notUsed==notUsed) : (notUsed=0, i=(sizeof(recent)/sizeof(recent[0])));
if(notUsed)
{
for(j=(sizeof(recent)/sizeof(recent[0]));j>1;j--)
{
recent[j-1] = recent[j-2];
}
recent[j-1] = number;
}
return notUsed;
}