1057. Stack (30)

​ 时间限制

​ 150 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:

key

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

我的第一次代码为简单模拟有几个测试点过不去，下面代码为我参考了三个网页的代码

AC代码为利用树状数组。。。

参考地址

参考地址

参考地址

代码如下：

#include<iostream>
#include<stack>



using namespace std;

stack<int> s;

#define lowbit(i) ((i)&(-i))
const int maxn=100010;
int c[maxn];
void update(int x,int v){
	for(int i=x;i<maxn;i+=lowbit(i)){
		c[i]+=v;
	}
}

int getsum(int x){
	int sum=0;
	for(int i=x;i>=1;i-=lowbit(i)){
		sum+=c[i];
	}
	return sum;
}
void PeekMedian(){
	int left=1,right=maxn,mid,k=(s.size()+1)/2;
	while(left<right){
		mid=(left+right)/2;
		if(getsum(mid)>=k){
			right=mid;
		}else{
			left=mid+1;
		}
	}
	printf("%d\n",left);
}
int main(){
	int n,temp;
	scanf("%d",&n);
	char str[20];
	for(int i=0;i<n;++i){
		scanf("%s",str);
		if(str[1]=='u'){
			scanf("%d",&temp);
			s.push(temp);
			update(temp,1);
		}else if(str[1]=='o'){
			if(!s.empty()){
				update(s.top(),-1);
				printf("%d\n",s.top());
				s.pop();
			}else{
				printf("Invalid\n");
			}
		}else{
			if(!s.empty()){
				PeekMedian();
			}else{
				printf("Invalid\n");;
			}
		}
	}
	return 0;
}