There is a simple hackerrank task, where I stuck on getting input phase.
Input code is simple (I'm using Objective-C)
int main(int argc, const char * argv[]) {
#autoreleasepool {
NSUInteger t;
scanf("%ld",&t);
int n,m,s;
int i = 0;
while (i < t) {
scanf("%d %d %d",&n,&m,&s);
printf("%d n=%d m=%d s=%d \n",i,n,m,s);
i++;
}
}
return 0;
}
But on a big test case with t=100, this small program freezes on step 33.
It looks like problem is in scanf function call,but cannot find it.
Here is testcase
I'm getting an error saying no matching function for call to 'getline' involving the getline(tokenizer, " "); Im not sure how to fix this, Ive tried including some other headers but I just keep coming up with more errors.
#include <iostream>
#include <fstream>
#include <cstring>
#include <sstream>
#include <string>
using namespace std;
char encrypt(char character, int offset);
int main(int argc, char *argv[]) {
ifstream inputFile;
string str;
string token;
bool debug = true;
int lineLength = 0, offset;
inputFile.open(argv[1]);
if (inputFile.fail())
cout << "File failed to open. \n";
istringstream tokenizer(str);
getline(tokenizer, " ");
offset = token.length();
while (getline(inputFile, str)){
lineLength = str.length();
for (int i = 0; i < lineLength; i++)
str.at(i) = encrypt(str.at(i), offset);
cout << str << endl;
}
inputFile.close();
return(0);
}
probably there is a smart way to do that , but anyway i get error on this :
-(int*)decimalBinary:(int)decimal
{
int i=0;
int *bin;
while (decimal!=0)
{
bin[i]=decimal%2;
decimal=decimal/2;
i++;
}
return bin;
}
on the modulo line . why ?
And whats the better way to get it to array ?
Declaring
int *bin;
sets aside space for a pointer but doesn't make it point to an object. It is crucial to initialize bin before using it.
To solve your problem you can declare an array bin[4] in caller function (int main) and then pass *bin to your calling function.
The following code is adapted from This answer on how to print an integer in binary format. Storing "binary digits" into an int array is added into the code below:
#include <stdio.h> /* printf */
#include <stdlib.h> /* strtol */
const char *byte_to_binary(long x);
int main(void)
{
long lVal;
int i, len, array[18];
char buf[18];
{ /* binary string to int */
char *tmp;
char *b = "11010111001010110";
lVal=strtol(b, &tmp, 2); //convert string in "base 2" format to long int
printf("%d\n", lVal);
}
{
printf("%s", byte_to_binary(lVal));
/* byte to binary string */
sprintf(buf,"%s", byte_to_binary(lVal));
}
len = strlen(buf);
for(i=0;i<len;i++)
{ //store binary digits into an array.
array[i] = (buf[i]-'0');
}
getchar();
return 0;
}
const char *byte_to_binary(long x)
{
static char b[17]; //16 bits plus '\0'
b[0] = '\0';
char *p = b;
int z;
for (z = 65536; z > 0; z >>= 1) //2^16
{
*p++ = (x & z) ? '1' : '0';
}
return b;
}
I am trying to divide my processors into groups then add the summation of each group
independently ... but I couldn't find the result correctly until now.
a simple example is as follows:
int main(int argc, char** argv)
{
int size, rank,i=0,localsum1=0,globalsum1=0,localsum2=0,globalsum2=0;
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&size);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
if(rank==0)
{
}
else if(rank==1)
{
localsum1 += 5;
MPI_Reduce(&localsum1,&globalsum1,2,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
}
else if(rank==2)
{
localsum2 += 10;
MPI_Reduce(&localsum2,&globalsum2,2,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
}
if(rank==0)
{
printf("globalsum1 = %d \n",globalsum1);
printf("globalsum2 = %d \n",globalsum2);
}
MPI_Finalize();
return (EXIT_SUCCESS);
}
I can't figure out what is missing here ... can anyone help?
MPI_Reduce is a collective operation. What that means is that all tasks in the participating communicator must make the MPI_Reduce() call. In the above, rank 0 never calls MPI_Reduce() so this program will hang as some of the other processors wait for participation from rank 0 which will never come.
Also, because it is a collective operation on the entire communicator, you need to do some work to partition the reduction. One way is just to reduce an array of ints, and have each processor contribute only to its element in the array:
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
int main(int argc, char** argv)
{
int size, rank;
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&size);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
int localsum[2] = {0,0};
int globalsum[2] = {0,0};
if(rank % 2 == 1)
{
localsum[0] += 5;
}
else if( rank > 0 && (rank % 2 == 0))
{
localsum[1] += 10;
}
MPI_Reduce(localsum,globalsum,2,MPI_INT,MPI_SUM,0,MPI_COMM_WORLD);
if(rank==0)
{
printf("globalsum1 = %d \n",globalsum[0]);
printf("globalsum2 = %d \n",globalsum[1]);
}
MPI_Finalize();
return (EXIT_SUCCESS);
}
where running now gives
$ mpicc -o reduce reduce.c
$ mpirun -np 3 ./reduce
globalsum1 = 5
globalsum2 = 10
Otherwise, you can create communicators that only connect the processors you want to be involved in each sum, and do the reductions within each commuicator. Below is a not-very-pretty way to do this. This is quite powerful in general but more complicated than the first solution:
#include <stdio.h>
#include <stdlib.h>
#include <mpi.h>
int main(int argc, char** argv)
{
int size, rank;
MPI_Init(&argc,&argv);
MPI_Comm_size(MPI_COMM_WORLD,&size);
MPI_Comm_rank(MPI_COMM_WORLD,&rank);
int localsum = 0;
int globalsum = 0;
MPI_Comm comm_evens_plus_root, comm_odds_plus_root;
MPI_Group grp_evens_plus_root, grp_odds_plus_root, grp_world;
MPI_Comm_group(MPI_COMM_WORLD, &grp_world);
int *ranks = malloc((size/2 + 1) * sizeof(rank));
int i,j;
for (i=1, j=0; i<size; i+=2, j+=1)
ranks[j] = i;
MPI_Group_excl(grp_world, j, ranks, &grp_evens_plus_root);
MPI_Comm_create(MPI_COMM_WORLD, grp_evens_plus_root, &comm_evens_plus_root);
for (i=2, j=0; i<size; i+=2, j+=1)
ranks[j] = i;
MPI_Group_excl(grp_world, j, ranks, &grp_odds_plus_root);
MPI_Comm_create(MPI_COMM_WORLD, grp_odds_plus_root, &comm_odds_plus_root);
free(ranks);
if(rank % 2 == 1)
{
localsum += 5;
MPI_Reduce(&localsum,&globalsum,1,MPI_INT,MPI_SUM,0,comm_odds_plus_root);
}
else if( rank > 0 && (rank % 2 == 0))
{
localsum += 10;
MPI_Reduce(&localsum,&globalsum,1,MPI_INT,MPI_SUM,0,comm_evens_plus_root);
}
if(rank==0)
{
MPI_Reduce(&localsum,&globalsum,1,MPI_INT,MPI_SUM,0,comm_odds_plus_root);
printf("globalsum1 = %d \n",globalsum);
MPI_Reduce(&localsum,&globalsum,1,MPI_INT,MPI_SUM,0,comm_evens_plus_root);
printf("globalsum2 = %d \n",globalsum);
}
MPI_Comm_free(&comm_odds_plus_root);
MPI_Comm_free(&comm_evens_plus_root);
MPI_Group_free(&grp_odds_plus_root);
MPI_Group_free(&grp_evens_plus_root);
MPI_Finalize();
return (EXIT_SUCCESS);
}
Running gives
$ mpicc -o reduce2 reduce2.c
$ mpirun -np 3 ./reduce
globalsum1 = 5
globalsum2 = 10
I'm trying to print the first line from each file but I think its outputting the address instead.
#include <fstream>
#include <iostream>
#include <cstdlib>
using namespace std;
void FirstLineFromFile(ifstream files[], size_t count)
{
const int BUFSIZE = 511;
char buf[BUFSIZE];
ifstream *end, *start;
for (start = files, end = files + count; start < end; start++)
{
cout << start->getline(buf, sizeof(buf)) << '\n';
}
}
streams should not be passed by value. This code passes an array of streams by value. You can try to pass a vector instead and interate over them.
void FirstLineFromFile(vector<ifstream*> files) {
for (int i=0; i<files.size(); ++i) {
string s;
getline(*files[i], s);
cout << s << endl;
}
}
ifstream->getline does not return a string as its return value. You need to print out the buffer that it has filled in a separate line.
for (start = files, end = files + count; start < end; start++)
{
start->getline(buf, sizeof(buf));
cout << buf << '\n';
}