CODEWITHSUNDEEP
cperformanceexecution
Angelo Berçacola
Angelo Berçacola

Reputation: 173

Is normal this code run SOO slow?

look at my code , it is running slow as a turtle, i running it under a forth generation i7... and it is realy slow to show off the result. does anybody have one ideia? or this should be a very slow execution!?

PS: the prourpose of the script is to find greatest product of four adjacent numbers in the same direction, actualy in this code i'm looking only for the up one

#include <stdio.h>
#include <math.h>

int main(){

        int A[20][20] = {
        {8,02,22,97,38,15,00,40,00,75,04,05,07,78,52,12,50,77,91,8},
        {49,49,99,40,17,81,18,57,60,87,17,40,98,43,69,48,04,56,62,00},
        {81,49,31,73,55,79,14,29,93,71,40,67,53,88,30,03,49,13,36,65},
        {52,70,95,23,04,60,11,42,69,24,68,56,01,32,56,71,37,02,36,91},
        {22,31,16,71,51,67,63,89,41,92,36,54,22,40,40,28,66,33,13,80},
        {24,47,32,60,99,03,45,02,44,75,33,53,78,36,84,20,35,17,12,50},
        {32,98,81,28,64,23,67,10,26,38,40,67,59,54,70,66,18,38,64,70},
        {67,26,20,68,02,62,12,20,95,63,94,39,63,8,40,91,66,49,94,21},
        {24,55,58,05,66,73,99,26,97,17,78,78,96,83,14,88,34,89,63,72},
        {21,36,23,9,75,00,76,44,20,45,35,14,00,61,33,97,34,31,33,95},
        {78,17,53,28,22,75,31,67,15,94,03,80,04,62,16,14,9,53,56,92},
        {16,39,05,42,96,35,31,47,55,58,88,24,00,17,54,24,36,29,85,57},
        {86,56,00,48,35,71,89,07,05,44,44,37,44,60,21,58,51,54,17,58},
        {19,80,81,68,05,94,47,69,28,73,92,13,86,52,17,77,04,89,55,40},
        {04,52,8,83,97,35,99,16,07,97,57,32,16,26,26,79,33,27,98,66},
        {88,36,68,87,57,62,20,72,03,46,33,67,46,55,12,32,63,93,53,69},
        {04,42,16,73,38,25,39,11,24,94,72,18,8,46,29,32,40,62,76,36},
        {20,69,36,41,72,30,23,88,34,62,99,69,82,67,59,85,74,04,36,16},
        {20,73,35,29,78,31,90,01,74,31,49,71,48,86,81,16,23,57,05,54},
        {01,70,54,71,83,51,54,69,16,92,33,48,61,43,52,01,89,19,67,48}};

        int x = 0 ,y = 0, radar_x = 0,radar_y = 0,maior = 0,produto = 1;


        while(x<=19){
                while(y<=19){
                        printf("%d %d \n",x,y);
                        // verredura pra cima
                        if(x - 3 >= 0){
                                radar_x = x-3;
                                while(radar_x >= x-3){
                                        produto*=A[x][y];
                                        radar_x ++ ;
                                }

                        }
                        if(produto > maior)
                                maior = produto;
                        produto = 1;
                        y++;
                }
                y=0;
                x++;
        }

        printf("%d",maior);


        return 0;

}

Upvotes: 0

Views: 112

Answers (3)

Rob11311
Rob11311

Reputation: 1416

Examining the inner for loop (written as a while) :

radar_x = x-3;
while(radar_x >= x-3){
    produto*=A[x][y];
    radar_x ++ ;
}

radar_x >= x-3 is true first time.. then radar_x is incremented... so this will likely loop until overflow occurs incrementing INT32_MAX (2147483647), when radar_x is suddenly < 0

You're looping at least 2 billion times, every time you start doing the multiplications.

The actual behaviour is underfined, a compiler writer is within their rights to say "the program is not C", so if you may overflow any adition should test "a < MAXINT - b" before executing a += b

Upvotes: 2

njzk2
njzk2

Reputation: 39386

This part of your code,

radar_x = x-3;
while(radar_x >= x-3){
   produto*=A[x][y];
   radar_x ++ ;
}

results in a quite long loop (possibly infinite, possibly undefined, possibly depending on your compiler), as x is not modified and radar_x is only incremented

To get the product of the 4 items in [x - 3, x], I would probably more simply do:

for (int radar_x = 0; radar_x < 4; radar_x++) {
    produto*=A[x - radar_x][y];
}

Edit

Remove already given answer, leave only alternative for loop

Upvotes: 0

architectpianist
architectpianist

Reputation: 2552

The reason it hasn't finished yet is because it will never technically stop. The third while loop is set to increment radar_x forever, with no upper bound. It's an easy mistake to make.

Just change it to while (radar_x <= x) to fix the problem.

Upvotes: 7

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