我用了 C++17 ，然后 Compile Error

#include <iostream>
#include <queue>

int main([[maybe_unused]] int argc, [[maybe_unused]] const char *argv[])
{
  std::priority_queue<int, std::vector<int>, std::greater<>> stack;
  int num;
  std::cin >> num;
  for (int i = 0; i < num; ++i) {
    int tmp;
    std::cin >> tmp;
    stack.push(tmp);
  }
  num = 0;
  while(stack.size() > 1) {
    auto tmp = stack.top();
    stack.pop();
    tmp += stack.top();
    stack.pop();
    stack.push(tmp);
    num += tmp;
  }
  std::cout << num << std::endl;
}

var
a,b:array[1..215000000]of integer;
n,i,j,s,m,f:longint;
begin
readln(n);for i:=1 to n do begin read(a[i]);inc(b[a[i]]);end;
while n>1 do begin
f:=0;i:=1;m:=0;
while f<2 do begin
while b[i]>0 do begin inc(f);inc(s,i);inc(m,i);dec(b[i]);end;
inc(i);
end;
inc(b[m]);dec(n);
end;
writeln(s);
end.

双队列
var
a,b:array[1..10010] of longint;
n,i,ans,ha,hb,tb,ne:longint;
procedure sort(l,r: longint);
var
i,j,x,y: longint;
begin
i:=l;
j:=r;
x:=a[(l+r) div 2];
repeat
while a[i]<x do
inc(i);
while x<a[j] do
dec(j);
if not(i>j) then
begin
y:=a[i];
a[i]:=a[j];
a[j]:=y;
inc(i);
j:=j-1;
end;
until i>j;
if l<j then
sort(l,j);
if i<r then
sort(i,r);
end;
begin
readln(n);
for i:=1 to n+1 do
begin
a[i]:=maxlongint;
b[i]:=maxlongint;
end;
for i:=1 to n do
read(a[i]);
sort(1,n);
ha:=1;hb:=1;tb:=0;ans:=0;
for i:=1 to n-1 do
begin
ne:=0;
if a[ha]<=b[hb] then begin
ne:=ne+a[ha];
inc(ha);
end
else begin
ne:=ne+b[hb];
inc(hb);
end;
if a[ha]<=b[hb] then begin
ne:=ne+a[ha];
inc(ha);
end
else begin
ne:=ne+b[hb];
inc(hb);
end;
inc(tb);
b[tb]:=ne;
ans:=ans+ne;
end;
write(ans);
end.

#include<iostream>
#include<algorithm>
#include<cstdio>
#include<cstdlib>
#include<cmath>
#include<ctime>
#include<string>
#include<cstring>
using namespace std;
int ans,n,a[10005];
int main()
{
ios::sync_with_stdio(false);
cin.tie(NULL);
cin>>n;
for(int i=1;i<=n;i++)cin>>a[i];
sort(a+1,a+n+1);
for(int i=1;i<n;i++)
{
int x;
x=a[i]+a[i+1];
ans+=x;
a[i+1]=x;
for(int j=i+2;j<=n;j++)
if(a[j]<a[j-1])swap(a[j],a[j-1]);
}
cout<<ans;
return 0;
}

使用STL：

#include<iostream>
#include<algorithm>
#include<queue>
using namespace std;

int main() {
    priority_queue<int> q;
    int t;
    cin >> t;
    for(int i = 0; i < t; i++) {
        int in;
        cin >> in;
        q.push(-in);
    }
    int ans = 0;
    for(int i = 0; i < t - 1; i++) {
        int w = 0;
        w = q.top();
        q.pop();
        w += q.top();
        q.pop();
        ans += w;
        q.push(w);
    }
    cout << -ans << endl;
    return 0;
}

#include<iostream>
#include<string>
#include<algorithm>
#include<set>
#include<vector>
using namespace std;

void calculate(vector<int>&s)
{
    int consume = 0;
    int merge_first = 0;
    int merge_two = 0;
    int sum = 0;
    vector<int>::iterator it;
    while ((it = min_element(s.begin(), s.end())) != s.end())
    {
        if (s.size() == 1)
        {
            printf("%d\n", sum);
            break;
        }
        if (it != s.end())
        {
            merge_first = *it;
            s.erase(it);
        }       
        it = min_element(s.begin(), s.end());
        if (it != s.end())
        {
            merge_two = *it;
            consume = merge_first + merge_two;
            sum += consume;
            s.erase(it);
            s.push_back(consume);
        }
    }
    
    
}
int main()
{

    //freopen("data.in", "r", stdin);
    //freopen("data.out", "w", stdout);
    int n;
    int num;
    cin >> n;
    vector<int> s;
    for (int i = 0; i < n; i++)
    {
        cin >> num;
        s.push_back(num);
    }

    calculate(s);
    
    
    return 0;
}

晕死，这么简单的题调了两天才发现时sort里的tot没有+2。。。

#include<cstdio>
#include<algorithm>
using namespace std;
int n,a[100001];
long long p=0;
void del(int& tot)
{
    for(int i=1;i<=tot;i++) a[i]=a[i+1];
    return;
}
int main()
{
    scanf("%d",&n);
    for(int i=1;i<=n;i++)
    scanf("%d",&a[i]);
    int tot=n-1;
    while(tot)
    {
        sort(a+1,a+tot+2);
        int sum=a[2]+a[1];
        a[2]=sum;
        a[1]=0;
        p+=sum;
        del(tot);
        tot--;
    }
    printf("%lld",p);
    return 0;
}

#include <cstdio>
#include <queue>
using namespace std;

priority_queue<int,deque<int>,greater<int> > q;
int ans;

inline int read(){
int f=1,s=0;
char c=getchar();
while(c<'0' || c>'9'){
if(c=='-')
f=-1;
c=getchar();
}
while(c>='0' && c<='9'){
s=s*10+c-'0';
c=getchar();
}
return f*s;
}

int main(){
int n,i,a,b;
scanf("%d",&n);
for(i=1;i<=n;i++)
q.push(read());
for(i=1;i<n;i++){
a=q.top();
q.pop();
b=q.top();
q.pop();
ans+=a+b;
q.push(a+b);
}
printf("%d\n",ans);
return 0;
}

经典的优先队列的问题
不多说咯

#include <iostream>
#include <cstdio>
#include <algorithm>
#include <cstring>
#include <iomanip>
#include <cstdlib>
#include <queue>
using namespace std;

const int INF=0x7fffff;
priority_queue<int,vector<int>,greater<int> > q;
int n;
long long ans=0;

int main()
{
    int a,b;
    int x;
    cin>>n;
    for(int i=1;i<=n;i++)
        cin>>x,q.push(x);
    for(int i=1;i<n;i++)
    {
        a=q.top();q.pop();
        b=q.top();q.pop();
        ans+=(a+b);
        q.push(a+b);
    }
    cout<<ans<<endl;
    return 0;
}
     

STL模板题 priority_queue
（附压行代码）

#include<bits/stdc++.h>
using namespace std;priority_queue<int>q;int main(){int n,x;scanf("%d",&n);while(n--)scanf("%d",&x),q.push(-x);x=q.top();q.pop();n=0;while(!q.empty())n+=x+q.top(),q.push(x+q.top()),q.pop(),x=q.top(),q.pop();printf("%d",-n);}

Ac

#include<bits/stdc++.h>
using namespace std;
int n;
int a[10000];
void cut(int k)
{
for(int i=0;i<n-k;i++)a[i]=a[i+1];
}
int main()
{
int sum=0;
cin>>n;
for(int i=0;i<n;i++)
{
cin>>a[i];
}

int k=0;
while(k+1<n)
{

sort(a,a+(n-k));
//for(int i=0;i<n-k;i++)cout<<a[i]<<" ";
//cout<<endl;
//cout<<"sum:"<<sum<<endl;
int s=a[0]+a[1];;
sum+=s;
a[1]=s;
cut(k);
k++;
}
cout<<sum<<endl;
return 0;
}

#include<bits/stdc++.h>
using namespace std;
int n;
int a[10000];
void cut(int k)
{
for(int i=0;i<n-k;i++)a[i]=a[i+1];
}
int main()
{
int sum=0;
cin>>n;
for(int i=0;i<n;i++)
{
cin>>a[i];
}

int k=0;
while(k+1<n)
{

sort(a,a+(n-k));
//for(int i=0;i<n-k;i++)cout<<a[i]<<" ";
//cout<<endl;
//cout<<"sum:"<<sum<<endl;
int s=a[0]+a[1];;
sum+=s;
a[1]=s;
cut(k);
k++;
}
cout<<sum<<endl;
return 0;
}

#include "stdio.h"
int main()
{
int a[10000],n,min1,min0;
int t = 0;
scanf("%d",&n);
for(int e = 0; e < n; e++)
scanf("%d",&a[e]);
min0 = a[0] < a[1] ? 1 : 0;
min1 = a[0] >= a[1] ? 1 : 0;
int p = n;
while(p-1)
{
for(int q = 0; q < n; q++)
{
if(a[min0] > a[q] && a[min1] > a[q])
{
min0 = min1;
min1 = q;
}
else if(a[min0] > a[q] && a[min1] <= a[q] && min1 != q)
min0 = q;
}
a[min1] = a[min1] + a[min0];
t += a[min1];
a[min0] = 200000000;
p--;
}
printf("%d",t);
Sleep(25000);
return 0;
}

优先队列！

#include<cstdio>
#include<queue>

using namespace std;
priority_queue<int> data;
int main()
{
    int n;
    scanf("%d",&n);
    
    for(int i=1,x;i<=n;i++)
    {
        scanf("%d",&x);
        data.push(-x);
    }
    int res=0;
    for(int i=1,tmp;i<n;i++)
    {
        tmp=data.top();
        res-=data.top();
        data.pop();
        tmp+=data.top();
        res-=data.top();
        data.pop();
        data.push(tmp);
    }
    printf("%d",res);
    return 0;
}

用priority_queue还是挺方便的

#include <iostream>
#include <algorithm>
#include <queue>
#include <vector>

using namespace std;

int main() {
    priority_queue<int, vector<int>, greater<int>> fruits;
    int total;
    cin >> total;
    for (int i = 0; i < total; ++i){
        int tmp;
        cin >> tmp;
        fruits.push(tmp);
    }
    int result = 0;
    while (fruits.size() != 1){
        int tmp = fruits.top();
        fruits.pop();
        int tmp2 = fruits.top();
        fruits.pop();
        fruits.push(tmp + tmp2);
        result += tmp + tmp2;
    }
    cout << result << endl;
    return 0;
}

没有必要对整个数组进行排序，只需单独考虑取前两位即可
#include <iostream>
using namespace std;
int n;
int num[10000];
void change(int x)
{
    int i,t,q;
    q=x;
    for (i=q+1;i<n;i++)
    {
        if (num[i]<num[q]) {
            q=i;
        }
    }
    t=num[x];
    num[x]=num[q];
    num[q]=t;
}
int main() {
    cin >> n;
    int i,j;
    int sum=0;
    for (i=0;i<n;i++)
        cin >> num[i];
    change(0); change(1);
    for (i=1;i<n;i++)
    {
        num[i]+=num[i-1];
        sum+=num[i];
        change(i);
        change(i+1);
    }
    cout << sum;
}

#include<iostream>
#include<algorithm>
#include<iomanip>
#include<cmath>
using namespace std;

int n,i,a[10005],s;
int main()
{
cin>>n;
for(i=1; i<=n; ++i) cin>>a[i];
sort(a+1,a+n+1);
while(n>1)
{
a[1]=a[1]+a[2];
s=s+a[1];
for (i=3; i<=n; ++i) a[i-1]=a[i];
n=n-1;
sort(a+1,a+n+1);
}

cout<<s;

return 0;
}

将数组由小到大排序之后，每次都取前两个的和，按大小插入到剩下的数组中，保证剩下的数组也是从小到达排序的。
注意的是每次取和之后剩下数组的起始位置就往后挪一位。
java代码：
import java.util.*;
import java.io.*;
public class tanxin {
public static void main(String[]args)throws IOException{
Scanner input=new Scanner(System.in);
int n=input.nextInt();
int[]s=new int[n];
int temp,j,sum=0;
for(int i=0;i<n;i++)
s[i]=input.nextInt();
if(n==1)
{
System.out.println(s[0]);
return;
}

Arrays.sort(s); //
for(int i=0;i<n-1;i++)
{
temp=s[i]+s[i+1];
sum+=temp;
for( j=i+1;j<n;j++)
{
if(s[j]<=temp)
s[j-1]=s[j];
else
break;
}
s[j-1]=temp;

}
System.out.println(sum);
}
}

#include <iostream>
#include <cstring>
#include <algorithm>
#include <queue> 
using namespace std;
int N,max_num,times=0; 
priority_queue<int, vector<int>, greater<int> > q;

int main(){
    int temp1,temp2,temp_sum,sum=0;
    cin>>N;
    for(int i = 1 ; i<=N ; i++){
        cin>>temp1;
        q.push(temp1);
    }
    while(!q.empty()){
        temp1=q.top();
        q.pop();
        if(q.empty()){
            break;
        }
        temp2=q.top();
        q.pop();
        temp_sum=temp1+temp2;
        sum+=temp_sum;
        q.push(temp_sum);       
    }
    cout<<sum<<endl;
    return 0;   
} 

贪心，使用优先队列，每次从队列中拿出2个最小的，ans累加其和，再把和作为新的元素放入队列中，直到队列长度为1.

代码如下：

```c++

#include <iostream>
#include <queue>

using namespace std;

int main(void)
{
long long ans = 0;
priority_queue<int,vector<int>,greater<int> > p;
int n,i,a;
cin>>n;

for(i = 0;i < n;i++){
cin>>a;
p.push(a);
}

while(p.size() > 1){
int m1,m2;
m1 = p.top();
p.pop();
m2 = p.top();
p.pop();

ans += m1 + m2;
p.push(m1 + m2);
}

cout<<ans;
return 0;
}