[Ural1306] Sequence Median（网上很多题解骗人，这才是对的！业界良心！）

血的教训：

1. 尽信题解，不如无题解！

2. C++ STL很坑爹。。

3. 题解很坑爹。。。

测试结果分析与比较：

#1是我自己写的，使用priority_queue，超内存：

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <queue>
using namespace std;
priority_queue <unsigned int> pq;
int main(){
    unsigned int n,i,x,s1,s2;
    scanf("%d",&n);
    if(n % 2 != 0){
        for(i=1;i<=n;i++){
            scanf("%d",&x);
            pq.push(x);
            if(pq.size() == n/2+2){
                pq.pop();
            }
        }
        printf("%.1lf
",(double)pq.top());
    }
    else{
        for(i=1;i<=n;i++){
            scanf("%d",&x);
            pq.push(x);
            if(pq.size() == n/2+2){
                pq.pop();
            }
        }
        s1 = pq.top();
        pq.pop();
        s2 = pq.top();
        printf("%.1lf
",(double)(s1+s2)/2);
    }
    return 0;
}

#2 from PegasusWang http://www.cnblogs.com/PegasusWang/archive/2013/03/23/2977597.html

使用priority_queue,同样超内存

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <queue> //for priority_queue
using namespace std;
int main()
{
priority_queue<unsigned int> ipq;
int n;
scanf("%d", &n);
unsigned int t;
for (int i = 1; i <= n / 2 + 1; ++i)
{
scanf("%u", &t);
ipq.push(t);
}
int tn = n / 2 + 2;
while (tn <= n)
{
scanf("%u", &t);
ipq.push(t);
++tn;
ipq.pop();
}
if (n & 1) //if n is odd
printf("%u.0 ", ipq.top());
else
{
int t1 = ipq.top();
ipq.pop();
printf("%.1f", (double)(t1 + ipq.top()) / 2);
}
return 0;
}

#3 from 不许偷懒啦小鬼 http://blog.csdn.net/yujuan_mao/article/details/7985424

使用priorty_queue，还是超内存

#include<cstdio>
#include<iostream>
#include<queue>
#include<vector>
#include<algorithm>
using namespace std;
int main(){
    unsigned int n,temp,i,j,k,m,x,y;
    priority_queue<unsigned int,vector<unsigned int>,greater<unsigned int> > Q;
    cin>>n;
    for(i=0;i<n;i++){
        scanf("%u",&m);
        Q.push(m);
        if(Q.size()>(n/2+1))
            Q.pop();
    }
    if(n%2)
        printf("%.1lf
",1.0*Q.top());
    else{
        x=Q.top();
        Q.pop();
        y=Q.top();
        printf("%.1lf
",1.0*(x+y)/2);
    }
    return 0;
}

#4 from http://www.zgxue.com/163/1639818.html

使用静态数组 +heap，AC

#include <iostream>
#include <algorithm>
#include <cstdio>
#include <cstring>
#include <vector>
#include <queue>
using namespace std;
const int maxn=250000;
int a[maxn/2+10];
int main()
{
    int n;double ans;
    while(scanf("%d",&n)!=EOF)
    {
       int num=0,x;
       for(int i=0;i<n/2+1;i++)
       scanf("%d",&a[i]);
       make_heap(a,a+n/2+1);
       for(int i=n/2+1;i<n;i++)
       {
           scanf("%d",&x);
           if(x<a[0])
           {
               pop_heap(a,a+n/2+1);
               a[n/2]=x;
               push_heap(a,a+n/2+1);
           }
       }
       if(n%2)
       {
           ans=(double)a[0];
           printf("%.1lf
",ans);
       }
       else
       {
           ans=(double)a[0];
           pop_heap(a,a+n/2+1);
           ans+=(double)a[0];
           printf("%.1lf
",ans/2.0);
       }

    }
    return 0;
}

 #5 自己写的，使用动态数组 + heap ，依然超内存

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
vector <unsigned int> v;
int main(){
    unsigned int n,i,x,s1,s2;
    scanf("%d",&n);
    if(n % 2 != 0){
        for(i=1;i<=n/2+1;i++){
            scanf("%d",&x);
            v.push_back(x);
        }
        make_heap(v.begin(),v.end());
        for(;i<=n;i++){
            scanf("%d",&x);
            v.push_back(x);
            push_heap(v.begin(),v.end());
            pop_heap(v.begin(),v.end());
            v.pop_back();
        }
        printf("%.1lf
",(double)v.front());
    }
    else{
        for(i=1;i<=n/2+1;i++){
            scanf("%d",&x);
            v.push_back(x);
        }
        make_heap(v.begin(),v.end());
        for(;i<=n;i++){
            scanf("%d",&x);
            v.push_back(x);
            push_heap(v.begin(),v.end());
            pop_heap(v.begin(),v.end());
            v.pop_back();
        }
        s1 = v.front();
        pop_heap(v.begin(),v.end());
        v.pop_back();
        s2 = v.front();
        printf("%.1lf
",(double)(s1+s2)/2);
    }
    return 0;
}

#6 自己写的，使用静态数组 +heap，AC

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <vector>
using namespace std;
unsigned int a[125005];
int main(){
    unsigned int n,i,x,s1,s2;
    scanf("%d",&n);
    if(n % 2 != 0){
        for(i=0;i<n/2+1;i++){
            scanf("%d",&a[i]);
        }
        make_heap(a,a+n/2+1);
        for(i=n/2+1;i<n;i++){
            scanf("%d",&x);
            a[n/2+1]=x;
            push_heap(a,a+n/2+2);
            pop_heap(a,a+n/2+2);
        }
        printf("%.1lf
",(double)a[0]);
    }
    else{
        for(i=0;i<n/2+1;i++){
            scanf("%d",&a[i]);
        }
        make_heap(a,a+n/2+1);
        for(i=n/2+1;i<n;i++){
            scanf("%d",&x);
            a[n/2+1]=x;
            push_heap(a,a+n/2+2);
            pop_heap(a,a+n/2+2);
        }
        s1 = a[0];
        pop_heap(a,a+n/2+1);
        s2 = a[0];
        printf("%.1lf
",(double)(s1+s2)/2);
    }
    return 0;
}

#7 from cz908640443 http://blog.163.com/cz_insane/blog/static/22046718520134234472659/

使用动态数组 + heap ，超内存

#include <iostream>
#include <algorithm>
#include <vector>
#include <cstdio>
using namespace std;

int i, n, temp, num[1];
long long ans;

int main(){
    cin>>n;
    cin>>num[0];
    vector<int> v(num, num + 1);
    for (i = 1; i < n / 2 + 1; i++){
        cin>>temp;
        v.push_back(temp);
        push_heap(v.begin(), v.end());
    }
    if (n % 2) {
        make_heap(v.begin(), v.end());
        for (i = n / 2 + 1; i < n; i++) {
            cin>>temp;
            v.push_back(temp);
            push_heap(v.begin(), v.end());
            pop_heap(v.begin(), v.end());
            v.pop_back();
        }
        printf("%.1lf
",(double)v.front());
    }
    else {
        make_heap(v.begin(), v.end());
        for (i = n / 2 + 1; i < n; i++) {
            cin>>temp;
            v.push_back(temp);
            push_heap(v.begin(), v.end());
            pop_heap(v.begin(), v.end());
            v.pop_back();
        }
        ans = v.front();
        pop_heap(v.begin(), v.end());
        v.pop_back();
        ans += v.front();
        printf("%.1lf
",(double)ans/2);
    }
    return 0;
}

从以上代码1~7 得到结论：priority_queue 1000KB+会超出内存，动态数组 + heap 1000KB+也会超出内存，只有静态数组 +heap 1000KB以下，不超内存

这是为什么呢？

The standard container adaptor priority_queue calls make_heap, push_heap and pop_heap automatically to maintain heap properties for a container.

 当初听说STL饱受诟病还不解，现在明白了，对于STL，如果没有领会其本质就乱用，得不偿失