【PAT】1057. Stack

考查点：分块思想，用hash记录push和pop情况，对于在线查找第k大的数可以用分块的思想对查找数的区间分成二次根个快

#define LOCAL
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <string>
#include <vector>
#include <map>
#include <set>
#include <queue>
#include <stack>
#define FOR(i, x, y) for(int i = x; i <= y; i++)
#define rFOR(i, x, y) for(int i = x; i >= y; i--)
#define MAXN 100010
#define oo 0x3f3f3f3f
using namespace std;
int st[MAXN];
int ta[MAXN];
int block[317];
const int N=316;
int main()
{
     #ifdef LOCAL
        freopen("data.in","r",stdin);
        freopen("data.out","w",stdout);
    #endif // LOCAL
    int top=-1;
    int n;
    char str[15];
    scanf("%d",&n);
    getchar();
    while(n--)
    {
        gets(str);
        if(strcmp(str,"Pop")==0){
            if(top==-1)printf("Invalid\n");
            else{
                int x=st[top--];
                ta[x]--;
                block[x/316]--;
                printf("%d\n",x);
            }
        }else if(strcmp(str,"PeekMedian")==0){
            if(top==-1)printf("Invalid\n");
            else{
                int cnt=top/2+1;
                int sum=0,i=0;
                while(sum+block[i]<cnt){
                    sum+=block[i++];
                }
                int num=i*N;
                while(sum+ta[num]<cnt){
                    sum+=ta[num++];
                }
                printf("%d\n",num);

            }
        }else{
            int len=strlen(str);
            int num=0;
            int d=5;
            while(d<len){
                num=num*10+str[d]-'0';
                d++;
            }
            ta[num]++;
            block[num/316]++;
            st[++top]=num;
        }
    }

    return 0;
}