Find N(3) largest number in K(10) numbers - c

Question

I want to find three largest number(area) from 10 numbers(scanf), I wrote this code, but only the largest number is correct when I run it, second and third largest number is wrong. So, I need help. any suggestions? Merry Christmas！
#include <stdio.h>
#define N 3
int main()
{
int i,j;
int area;
int maxArea[N];
int empty = N;
for(j=0;j<10;j=j+1)
{
printf("Input:");
scanf("%d",&area);
printf("\n");
if(empty > 0)
{
maxArea[N-empty]=area;
empty=empty-1;
}
else
{
for(i=0; i < N; i=i+1)
{
if(area>maxArea[i])
{
maxArea[i]=area;
break;
}
}
}
}
printf("Area1=%d\n",maxArea[0]);
printf("Area2=%d\n",maxArea[1]);
printf("Area3=%d\n",maxArea[2]);
}

Answer 1

#include <stdio.h>
#include <limits.h>
#include <string.h>
#define N 3
int main(){
int i,j;
int area;
int maxArea[N];
for(i=0;i<N;++i)
maxArea[i]=INT_MIN;
for(j=0;j<10;++j){
printf("Input:");
scanf("%d",&area);
printf("\n");
for(i = 0;i<N && i <= j;++i){
if(area > maxArea[i]){
memmove(&maxArea[i+1], &maxArea[i], (N-i-1)*sizeof(*maxArea));
maxArea[i] = area;
break;
}
}
}
printf("Area1=%d\n", maxArea[0]);
printf("Area2=%d\n", maxArea[1]);
printf("Area3=%d\n", maxArea[2]);
return 0;
}

Answer 2

Firstly you should initialize all the array elements to zero.
Also, your code does not work correctly since you only check for the first element in the array that is lesser than the new element.
If the array has 6, 3, 2 and the new element is 7, then 7 shall pop out 6 from the array and the array shall become 7, 3, 2. Instead it should have been 7, 6, 3.
You should pop out the lowest number in the array.
In the general case a minheap would be the best resort. (for k largest elements)

Answer 3

I just want to show you a different approach, you have to decide for yourself what is easier;
First I initialize maxArea with the smallest possible integer. This way I don't need special handling if it does not contain 3 numbers yet. Any number will simply be larger then MIN_INT, so it will be replaced automatically.
for(i=0; i < N; i++)
{
maxArea[i]=MIN_INT;
}
In the loop, I swap area with the old maximum value, and I keep running the loop, so the old value will be reused for the other max values.
for(j=0;j<10;j=j+1)
{
printf("Input:");
scanf("%d",&area);
printf("\n");
for(i=0; i < N; i++)
{
if(area>maxArea[i])
{
// swap both
int temp=maxArea[i];
maxArea[i]=area;
area=temp;
}
}
}
Note that this is not very optimized, but it might be better to read what is happening. maxArea[0] will always be the largers, maxArea[1] the next and so on.
for example if the array is [6, 3, 2], and the new area is 5;
nothing will happen in the first loop, because 5 is smaller than 6.
In the second loop (i=1), the array will become [6, 5, 2] and area will be 3.
In the third loop, the array will become [6, 5, 3], and area will be 2, (but that 2 will not be used any more).