Merge Sort (Array)

This is a discussion on Merge Sort (Array) within the C++ Programming forums, part of the General Programming Boards category; Cannot see what is wrong with my code: Currently trying to sort an array using merge sort. Code: #include <iostream> ...

  1. #1
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    Exclamation Merge Sort (Array)

    Cannot see what is wrong with my code: Currently trying to sort an array using merge sort.

    Code:
    #include <iostream>
    
    #define SIZE 4
    
    void mergeSort(float arraySorted[], float arrayTemp[], int LHS, int RHS);
    void mergeBack(float arraySorted[], float arrayTemp[], int LHS, int middle, int RHS);
    
    void main(){
    	
    	int Counter=0;
    	float arrayOne[SIZE] = {65, -72, 54, 238};
    	float arrayTwo[SIZE];
    
    
    
    		for (Counter=SIZE-1;Counter>=0;Counter--){
    			std::cout << arrayOne[Counter] << std::endl;
    		}
    
    	std::cout << "Something about sorting:" << std::endl;
    	mergeSort(arrayOne, arrayTwo, 0, SIZE-1);
    
    		for (Counter=SIZE-1;Counter>=0;Counter--){
    			std::cout << arrayOne[Counter] << std::endl;
    		}
    
    
    	std::cout << "Blah" << std::endl;
    }
    
    void mergeSort(float arraySorted[], float arrayTemp[], int LHS, int RHS){
    
    	int Counter, middle;
    
    		if (RHS > LHS){
    			middle = (LHS + RHS) / 2;
    
    			mergeSort(arraySorted, arrayTemp, LHS, middle);
    			mergeSort(arraySorted, arrayTemp, (middle+1), RHS);
    
    			mergeBack(arraySorted, arrayTemp, LHS, middle, RHS);
    		}
    
    }
    
    void mergeBack(float arraySorted[], float arrayTemp[], int LHS, int middle, int RHS){
    
    	int LHSEnd, arraySize, arrayPosition, Counter = 0;
    
    	LHSEnd = (middle -1);
    	arrayPosition = (LHS);
    
    		while ((LHS <= LHSEnd) && (middle <= RHS)){
    			if (arraySorted[LHS] <= arraySorted[middle]){
    				
    				arrayTemp[arrayPosition] = arraySorted[LHS];
    				arrayPosition = arrayPosition + 1;
    				LHS = LHS + 1;
    
    			}else{
    
    				arrayTemp[arrayPosition] = arraySorted[LHS];
    				arrayPosition = arrayPosition + 1;
    				middle = middle + 1;
    
    			}
    		}
    
    		while(LHS <= LHSEnd){
    			
    			arrayTemp[arrayPosition] = arraySorted[LHS];
    			LHS = LHS + 1;
    			arrayPosition = arrayPosition + 1;
    
    		}
    
    		while(middle <= RHS){
    
    			arrayTemp[arrayPosition] = arraySorted[middle];
    			middle = middle + 1;
    			arrayPosition = arrayPosition + 1;
    		
    		}
    		
    		LHS=-SIZE-1;
    		for(Counter=SIZE;Counter>=0;Counter--){
    			arraySorted[LHS] = arrayTemp[LHS];
    			LHS = LHS + 1;
    		}
    
    }
    Also I am unsure of how to work out the Big-0 or how many procedures it requires to work this out.

    If anyone can help me with either of my problems I would be very grateful.

  2. #2
    C++まいる!Cをこわせ! Elysia's Avatar
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    Re Big-Oh: work your way through main (should be int main, btw). For each statement, add the Big-Oh orders. When adding them, remember that only the highest one matters.
    For any nested loops, multiply the order.

    For any function calls, calculate the Big-Oh for that function. Then you know that the function call will be of that order.
    Eg, if merge_sort is O^2 and the rest of the code in main is O, then it is O + O^2 = O^2.
    Repeat for ALL functions.
    Quote Originally Posted by Adak View Post
    io.h certainly IS included in some modern compilers. It is no longer part of the standard for C, but it is nevertheless, included in the very latest Pelles C versions.
    Quote Originally Posted by Salem View Post
    You mean it's included as a crutch to help ancient programmers limp along without them having to relearn too much.

    Outside of your DOS world, your header file is meaningless.

  3. #3
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    Thanks for the insight to Big-Oh: Do you have any idea what is wrong with my script, it just seems to outpute the same array in the same order after 'sort'. Cannot work out why...

  4. #4
    Algorithm Dissector iMalc's Avatar
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    You've got a copy and paste bug here:
    Code:
    				arrayTemp[arrayPosition] = arraySorted[LHS];
    				arrayPosition = arrayPosition + 1;
    				middle = middle + 1;
    I would replace those three lines with just:
    Code:
    arrayTemp[arrayPosition++] = arraySorted[middle++];
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