PAT 1057 Stack

最新推荐文章于 2020-10-05 23:39:21 发布

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最新推荐文章于 2020-10-05 23:39:21 发布

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原文链接：http://www.cnblogs.com/mr-stn/p/9574616.html

本文介绍了一个特殊的数据结构——栈，并在此基础上增加了返回当前所有元素中位数的功能。通过使用辅助数据结构，文章详细说明了如何高效地完成元素的插入、删除及中位数查找等操作。

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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

Input Specification:

Each input file contains one test case. For each case, the first line contains a positive integer

Push key
Pop
PeekMedian

where key is a positive integer no more than $1.$

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

 1 #include<iostream>
 2 #include<vector>
 3 #include<algorithm>
 4 #include<stack>
 5 #define lowbit(x) ((x)&(-x))
 6 using namespace std;
 7 
 8 vector<int> C(100010, 0);
 9  
10 stack<int> s;
11 int getSum(int x){
12   int sum=0;
13   for(int i=x; i>0; i -= lowbit(i))
14     sum += C[i];
15   return sum;
16 }
17 
18 void update(int x, int v){
19   for(int i=x; i<100010; i += lowbit(i))
20     C[i] += v;
21 }
22 
23 void Media(){
24   int l=1, r=100010;
25   int k=(s.size()+1)/2;
26   while(l<r){
27     int mid=(l+r)/2;
28     if(getSum(mid)>=k) r=mid;
29     else if(getSum(mid)<k) l=mid+1;
30   }
31   printf("%d\n", l);
32 }
33 int main(){
34   int n, i;
35   scanf("%d", &n);
36  
37   for(i=0; i<n; i++){
38     char ch[15];
39     scanf("%s", ch);
40     if(ch[1]=='o'){
41       if(!s.size()) printf("Invalid\n");
42       else{
43         printf("%d\n", s.top());
44         update(s.top(), -1);
45         s.pop();
46       }
47     }else if(ch[1]=='u'){
48       int temp;
49       scanf("%d", &temp);
50       s.push(temp);
51       update(temp, 1);
52     }else{
53       if(s.size()) Media();
54       else printf("Invalid\n");
55     }
56   }
57   return 0;
58 }