Simple Queue

Simple Queue

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Problem

Implement a queue. Input some number means action.(End with EOF) 1
means push into the queue. Promise that another integer will follow
it, meaning the value to push. If the queue is full, print Push
Failed. The queue is full. If the queue is not full, push it into the
queue. (Output nothing) 0 means pop the front value of the queue.
Print the value that was just popped out. If the queue is empty, print
Pop Failed. The queue is empty. If the queue is not empty, print the
value In this assignment, a queue with a size of 10 is enough. Sample

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Input

0
1 1
1 2
1 3
1 4
1 5
1 6
1 7
1 8
1 9
1 10
1 11
0
0
0
0
0
0
0
0
0

Sample Output

Pop Failed. The queue is empty.
Push Failed. The queue is full. 
1 
2 
3 
4 
5 
6 
7 
8 
9 
10 
Pop Failed. The queue is empty. 

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Hint (Circular Queue)

If you don’t want to see my BB, you can skip this part or just go to
wikipedia to see a very nice gif explaining this.

Queue is a data structure that is FIFO(First In First Out), which means the data first to be pushed, will be first popped.
Generally, we use an array to implement circular queue.
For example, int my_queue[11];.
Then, we should know where the front/rear is. So we get two “pointer” to store the index of the the front/rear.
int front_index = 0, rear_index = 0;
Then with this, we know their position so we can modify it.
How to push ?
my_queue[rear_index++] = value; Set the value and Move the rear_index.
How to pop ?
front_index++; Move the front_index. Now we cannot access that value, so it seems we popped(delete) it.
What is Circular ?
F for front, R for rear.
This queue is full. (Will explain why in the following part)

queue : [1,2,3,4,5,6,7,8,9,10]

1 2 3 4 5 6 7 8 9 10 N
^ ^
F R

Pop 2 times, then we have

queue : [3,4,5,6,7,8,9,10]

1 2 3 4 5 6 7 8 9 10 N
^ ^
F R

Push 5 and 6

queue : [3,4,5,6,7,8,9,10,5,6]

6 2 3 4 5 6 7 8 9 10 5
^ ^
R F
Then you see, rear_index reached the end but came out again from the other side. That’s it, a circle indeed.
To implement this, when the index change, you should write index %= 11;.
Why 11 but not 10 ?
Here, though the length of the array is 11, only 10 spaces can be used.
We have to know if it is full or empty. Here, when front_index == rear_index we think it’s empty, when rear_index + 1 == front_index we think it’s full.
Empty

N N N N N N N N N N N
^
F/R

Full

1 2 3 4 5 6 7 8 9 10 N
^ ^
F R
In this way of implementation, my_queue[rear_index] is always unreachable. If it points to a position that has a data, then we cannot know if it is empty when front_index == rear_index.
(Certainly, there are some other ways to implement without this limitation)
This is why we can only use 10 spaces in a 11-long array.
If you still have no idea about this, search it yourself.

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ANSWER

include<stdio.h>
int main()
{
  int a,b,c=0;
  int x[10]={0};
  while(scanf("%d",&a)!=EOF)
  {
    if(a==1)
    {
      scanf("%d",&b);
      if(c>=10)
        printf("Push Failed. The queue is full.\n");
      else
        x[c++]=b;
    }
    if(a==0)
    {
      if(c<=0)
        printf("Pop Failed. The queue is empty.\n");
      else{
        printf("%d\n",x[0]);
        for(b=1;b<=9;b++)
          x[b-1]=x[b];
        c--;
      }
    }
  }
  return 0;
}