1057. Stack (30)

清疚 2022-05-31 14:27 135阅读 0赞

Stack is one of the most fundamental data structures, which is based on the principle of Last In First Out (LIFO). The basic operations include Push (inserting an element onto the top position) and Pop (deleting the top element). Now you are supposed to implement a stack with an extra operation: PeekMedian -- return the median value of all the elements in the stack. With N elements, the median value is defined to be the (N/2)-th smallest element if N is even, or ((N+1)/2)-th if N is odd.

**Input Specification:**

Each input file contains one test case. For each case, the first line contains a positive integer N (<= 105). Then N lines follow, each contains a command in one of the following 3 formats:

Push *key*  
Pop  
PeekMedian

where *key* is a positive integer no more than 105.

**Output Specification:**

For each Push command, insert *key* into the stack and output nothing. For each Pop or PeekMedian command, print in a line the corresponding returned value. If the command is invalid, print "Invalid" instead.

**Sample Input:**

17
    Pop
    PeekMedian
    Push 3
    PeekMedian
    Push 2
    PeekMedian
    Push 1
    PeekMedian
    Pop
    Pop
    Push 5
    Push 4
    PeekMedian
    Pop
    Pop
    Pop
    Pop

**Sample Output:**

Invalid
    Invalid
    3
    2
    2
    1
    2
    4
    4
    5
    3
    Invalid

--------------------

题目大意：

代码：

#include<stdio.h>
    #include<string.h>
    int s[100001],c[100001],top=0;
    int lowbit(int i)
    {
        return i&(-i);
    }
    void update(int x,int y)
    {
        for(int i=x;i<100001;i+=lowbit(i))
        {
            c[i]+=y;
        }
    }
    int getsum(int x)
    {
        int sum=0;
        for(int i=x;i>=1;i-=lowbit(i))
        {
            sum+=c[i];
        }
        return sum;
    }
    void PeekMedian()
    {
        int i=1,j=100001,k=(top+1)/2;
        while(i<j)
        {
            int mind=(i+j)/2;
            if(getsum(mind)>=k)
            {
                j=mind;
            }
            else
            {
                i=mind+1;
            }
        }
        printf("%d\n",i);
    }
    int main()
    {
        int i,j,n,m,k,t;
        char operation[15];
        scanf("%d",&n);
        for(i=0;i<n;i++)
        {
            scanf("%s",operation);
            if(strcmp(operation,"Pop")==0)
            {
                if(top==0)
                {
                    printf("Invalid\n");
                }
                else
                {
                    printf("%d\n",s[top-1]);
                    update(s[top-1],-1);
                    top--;
                }
            }
            else if(strcmp(operation,"Push")==0)
            {
                scanf("%d",&s[top++]);
                update(s[top-1],1);
            }
            else
            {
                if(top==1)
                {
                    printf("%d\n",s[0]);
                }
                else if(top>1)
                {
                    PeekMedian();
                }
                else
                {
                    printf("Invalid\n");
                }
            }
        }
        return 0;
    }