1057. Stack (30)
时间限制
100 ms
内存限制
65536 kB
代码长度限制
16000 B
判题程序
Standard
作者
CHEN, Yue
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
#define DeBUG
#include <iostream>
#include <cstdio>
#include <cstring>
#include <cmath>
#include <cstdlib>
#include <algorithm>
#include <vector>
#include <stack>
#include <queue>
#include <string>
#include <set>
#include <sstream>
#include <map>
#include <list>
#include <bitset>
using namespace std ;
#define zero {0}
#define INF 0x3f3f3f3f
#define EPS 1e-6
#define TRUE true
#define FALSE false
typedef long long LL;
const double PI = acos(-1.0);
//#pragma comment(linker, "/STACK:102400000,102400000")
inline int sgn(double x) {return fabs(x) < EPS ? 0 : (x < 0 ? -1 : 1);}
struct BinTree
{
static const int MAXN = 100010;
std::vector<int> a;
BinTree()
{
a = std::vector<int>(MAXN, 0);
}
int lowbit(int t)
{
return t & (-t);
}
void update(int t, int d)
{
while (t <= MAXN)
{
a[t] += d;
t += lowbit(t);
}
}
int getsum(int t)
{
int sum(0);
while (t > 0)
{
sum += a[t];
t -= lowbit(t);
}
return sum;
}
int find(int val, int l = 0, int h = MAXN - 1)
{
if (l == h)
return l;
int mid = (l + h) / 2;
if (getsum(mid) < val)
return find(val, mid + 1, h);
else
return find(val, l, mid);
}
};
BinTree tree;
int main()
{
#ifdef DeBUGs
freopen("/Users/sky/Documents/sublime project/in.txt", "r", stdin);
#endif
int N;
scanf("%d", &N);
char str[20];
int n(0);
stack<int>stk;
while (N--)
{
scanf("%s", str);
switch (str[1])
{
case 'o':
if (stk.empty())
{
printf("Invalid\n");
}
else
{
n = stk.top();
printf("%d\n", n);
stk.pop();
tree.update(n, -1);
}
break;
case 'u':
scanf("%d", &n);
stk.push(n);
tree.update(n, 1);
break;
case 'e':
if (stk.empty())
printf("Invalid\n");
else
{
printf("%d\n", tree.find((stk.size() + 1) / 2));
}
break;
}
}
return 0;
}