PAT1057 stack (block Thought)

1057 Stack (30 minutes)

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

Ideas: The block of Thought, dividing the data into data range sqrt (N) blocks, rounding the number of elements in each block does not exceed sqrt (N) rounding, block [i] of each recording containing the number of elements 
number table [x] of the recording elements appear

 1 #include <iostream>
 2 #include <algorithm>
 3 #include <cstring>
 4 #include <stack> 
 5 #include <cmath>
 6 
 7 using namespace std ;
 8 
 9 const int N = 100010,K = 316 ;
10 int block[K+1] ;
11 int table[N] ;
12 
13 stack<int> stk ;
14 
15 int peekMedian(int cnt){
16     int sum = 0 ;
17     if(cnt%2){
18         cnt = (cnt+1)/2 ;
19     }else{
20         cnt /= 2 ;
21     }
22     int i = 0,idx = cnt ;
23     for(;i<K;i++){
24         sum += block[i] ;
25         if(sum>=cnt){
26             break ;
27         }
28         idx -= block[i] ;
29     }
30     for(int j=i*K;j<K*(K+1);j++){
31         if(idx<=table[j]){
32             return j ;
33         }
34         idx -= table[j] ;
35     }
36 }
37 
38 int main(){
39     int n ;
40     cin >> n ;
41     
42     int cnt = 0 ;
43     while(n--){
44         string cmd ;
45         cin >> cmd ;
46         
47         if(cmd == "Pop"){
48             if(stk.empty()){
49                 cout << "Invalid" << endl ;
50             }else{
51                 int ele = stk.top() ;
52                 stk.pop() ;
53                 cout << ele << endl ;
54                 block[ele/K] -- ;
55                 table[ele] -- ;
56                 cnt -- ;    
57             }
58         }else if(cmd == "Push"){
59             int x ;
60             cin >> x ;
61             stk.push(x) ;
62             block[x/K] ++ ;
63             table[x] ++ ;
64             cnt ++ ;
65         }else{
66             if(stk.empty()){
67                 cout << "Invalid" << endl ;
68             }else{
69                 cout << peekMedian(cnt) << endl ;
70             }
71         }
72     }
73     
74     return 0 ;
75     
76 }

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