Re: any suggestion to improve the following code?

Barry <>
Thu, 03 Jan 2008 10:21:52 +0800
Fei Liu wrote:

#include <iostream>
#include <fstream>
#include <algorithm>

using namespace std;

#include <ext/hash_map>
using namespace __gnu_cxx;

#include <boost/filesystem/convenience.hpp>

hash_map<unsigned int, unsigned int, hash<unsigned int> > steps;

// Computes number of steps for number n according
// to Collatz Conjecture (3n+1 problem)
// To speed things up, results are book kept, saved/restored
// when program starts/finishes.
// In the recursively computing function, the steps to finish a
// a number is always memorized and retrieved on demand.
unsigned int compute_steps(int n){
    // shortcut to retrieve memorized steps[n]
        return steps[n];
    if(n == 1) return 1;
        n = 3*n+1;
        n = n/2;
    cout << ' ' << n;
    // shortcut to memorize steps[n]
    steps[n] = compute_steps(n);
    return steps[n] + 1;

int main(){
    boost::filesystem::path file("record_h.txt");

    unsigned int two[2];
        ifstream inf("record_h.txt", ios::binary);
        while( *)two, 2*sizeof(unsigned int)))
            steps[two[0]] = two[1];

no need to call fstream::close explictly.
the destructor will handle this well.


using Boost.FileSystem here just to detect a file exists or not may be
overkill, and after knowing that the file does exist, you can't
guarantee that th opening of the file will be successful.

so just

std::string const file_path = "record_h.txt";
std::ifstream inf(file_path, ios_base::binary);
if (!inf)
   // report fail
   return EXIT_FAILURE;
   // read the file

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