Thread: Vector Image Enlarge

  1. #1
    Registered User
    Join Date
    Apr 2006

    Vector Image Enlarge

    I'm trying to get better at C++ so I have been doing some of the challenges at topcoder.

    This was the problem

    Given an image as a vector <string>, scale it up by factor. That is, if the original image is M x N, the scaled image should be M*factor x N*factor. Each character in the input vector <string> should be represented by factor x factor of the same character in the output (see examples).



    { "aaabbbccc",
    "ggghhhiii" }

    Here is my solution but 4 loops seems too much. Can anybody show me what I could do better? Thanks

    #include <vector>
    #include <iostream>
    using namespace std;
    class ImageEnlarger{
    vector <string> enlarge(vector <string> image, int factor){
      string tempImage="", tempReturn="";  
      vector <string> returnImage;  
      for(int i=0;i<image.size();i++){  
        for(int j=0;j<factor;j++){ 
          for(int k=0;k<tempImage.length();k++){    
            for(int z=0;z<factor;z++){      
            }//end for
          }//end for       
         }//end for
      }//end for
      return returnImage;
    }//end enlarge
    };//end class

  2. #2
    Registered User
    Join Date
    May 2006
    Here's my take on it, although I didn't bother to make it a function or put it in a class or anything. I'm sure the scaling algorithm could be better still...and I think I miss-used the size_t type, but I'm still in the process of learning myself

    EDIT: I decided to put it in function form like you did, so I'm replacing the old code with the new code. I'm just not sure it's a good idea to be passing and returning a vector this way...I believe I read that it's more efficient to pass/return an iterator instead.

    #include <iostream>
    #include <string>
    #include <vector>
    using namespace std;
    vector<string> Enlarge(const vector<string> &inImage, int scaleFactor)
    	vector<string> outImage;
    	size_t inWidth = inImage[0].length();  // first string determines width of image
    	size_t inHeight = inImage.size();
    	size_t outWidth = inWidth * scaleFactor;
    	size_t outHeight = inHeight * scaleFactor;
    	double step = 1.0 / scaleFactor;
    	for (size_t y = 0; y != outHeight; ++y)
    		string temp;
    		size_t yIndex = static_cast<size_t>(step * y);
    		for (size_t x = 0; x != outWidth; ++x)
    			size_t xIndex = static_cast<size_t>(step * x);
    			temp += inImage[yIndex][xIndex];
    	return outImage;
    int main()
    	char *data[] = {"abc", "def", "ghi"};
    	size_t dataSize = sizeof(data) / sizeof(char *);
    	vector<string> image(data, data + dataSize);
    	vector<string> scaledImage;
    	scaledImage = Enlarge(image, 3);
    	// Output both image and scaledImage vectors
    	copy(image.begin(), image.end(), ostream_iterator<string>(cout, "\n"));
    	cout << endl;
    	copy(scaledImage.begin(), scaledImage.end(), ostream_iterator<string>(cout, "\n"));
    	return 0;
    Last edited by veecee; 05-20-2006 at 08:11 PM.

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