SO EASY
var
w,n,i,j,ans:longint;
a:array[1..50000]of 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
read(w,n);for i:=1 to n do read(a[i]);
sort(1,n);
i:=1;j:=n;
while i<=j do
begin
if a[i]+a[j]<=w then
begin
i:=i+1;
j:=j-1;
ans:=ans+1;
end
else
begin
j:=j-1;
ans:=ans+1;
end;
end;
write(ans);
end.

program qs;
var
p,n,b,c,s,w:longint;
a:array[1..30005]of longint;
procedure qs(l,r:longint);
var
i,j,m,t:longint;
begin
i:=l;j:=r;m:=a[l];
repeat
while a[i]<m do inc(i);
while a[j]>m do dec(j);
if i<=j then
begin
t:=a[i];
a[i]:=a[j];
a[j]:=t;
inc(i);dec(j);
end;
until i>j;
if l<j then qs(l,j);
if i<r then qs(i,r);
end;
begin
c:=0;
readln(w,n);
for p:=1 to n do
read(a[p]);
qs(1,n);
b:=n;s:=1;
while s<=b do
begin
if a[s]+a[b]<=w then
begin
c:=c+1;dec(b);inc(s);
end
else
begin
c:=c+1;dec(b);
end;
end;
write(c);
end.

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <functional>
using namespace std;
const int maxn=30005;
int main()
{
int maxWeight,count;
int weight[maxn];
scanf("%d%d",&maxWeight,&count);
for(int i=0;i<count;i++) scanf("%d",&weight[i]);
sort(weight,weight+count,greater<int>());

int head=0,tail=count-1;
int ans=0;
while(head<tail) {
if(weight[head]+weight[tail]<=maxWeight) tail--;
head++;
ans++;
}
if(head==tail) ans++;
printf("%d",ans);
return 0;
}

var i,j,v,n,m,k,s,t:longint;
a:array[1..100]of longint;
procedure q(l,r:longint);
var i,j,m,p:longint;
begin
i:=l;j:=r;
m:=a[(l+r)div 2];
repeat
while a[i]<m do inc(i);
while a[j]>m do dec(j);
if i<=j then begin
p:=a[i];a[i]:=a[j];a[j]:=p;
inc(i);dec(j);
end;
until i>j;
if l<j then q(l,j);
if i<r then q(i,r);
end;
begin
readln(m,n);
for i:=1 to n do readln(a[i]); s:=0;
q(1,n);
v:=1;
k:=n;
while n>0 do
begin
if a[v]+a[k]<=100 then begin s:=s+1;v:=v+1;k:=k-1;n:=n-2;end
else begin s:=s+1;k:=k-1;n:=n-1;end;
end;
writeln(s);
end.

var
w,n,i,m,j:integer;
p:array[0..30000] of integer;
procedure qsort(l,r:integer);
var
i,j,k,x:integer;
begin
k:=random(r-l+1)+l;
x:=p[k];
i:=l;
j:=r;
repeat
while p[i]<x do i:=i+1;
while p[j]>x do j:=j-1;
if i<=j then
begin
p[0]:=p[i];
p[i]:=p[j];
p[j]:=p[0];
i:=i+1;
j:=j-1;
end;
until i>j;
if i<r then qsort(i,r);
if j>l then qsort(l,j);
end;
begin
readln(w);
readln(n);
for i:=1 to n do
readln(p[i]);
qsort(1,n);
i:=0;
m:=n;
j:=1;
repeat
if p[m]+p[j]<=w then
begin
i:=i+1;
m:=m-1;
j:=j+1;
end
else
begin
i:=i+1;
m:=m-1;
end;
until m<j;
writeln(i);
end.

测试数据 #0: Accepted, time = 0 ms, mem = 932 KiB, score = 10
测试数据 #1: Accepted, time = 0 ms, mem = 932 KiB, score = 10
测试数据 #2: Accepted, time = 0 ms, mem = 932 KiB, score = 10
测试数据 #3: Accepted, time = 0 ms, mem = 928 KiB, score = 10
测试数据 #4: Accepted, time = 0 ms, mem = 932 KiB, score = 10
测试数据 #5: Accepted, time = 0 ms, mem = 932 KiB, score = 10
测试数据 #6: Accepted, time = 15 ms, mem = 932 KiB, score = 10
测试数据 #7: Accepted, time = 15 ms, mem = 932 KiB, score = 10
测试数据 #8: Accepted, time = 15 ms, mem = 932 KiB, score = 10
测试数据 #9: Accepted, time = 0 ms, mem = 928 KiB, score = 10
Accepted, time = 45 ms, mem = 932 KiB, score = 100
快排 水题一道

快排+大小比对
var a:array[1..30000] of longint;
w,n,i,j,t:longint;
procedure kp(l,r:longint);
var i,j,mid,t:longint;
begin
i:=l;j:=r;
mid:=a[(i+j) div 2];
repeat
while a[i]<mid do inc(i);
while a[j]>mid do dec(j);
if i<=j then
begin
t:=a[i];a[i]:=a[j];a[j]:=t;
inc(i);dec(j);
end;
until i>j;
if i<r then kp(i,r);
if l<j then kp(l,j);
end;
begin
read(w);
read(n);
for i:=1 to n do
read(a[i]);
kp(1,n);
i:=1;j:=n;
while i<=j do
begin
if a[i]+a[j]<=w then begin inc(i);dec(j);end
else dec(j);
inc(t);
end;
write(t);
end.

测试数据 #0: Accepted, time = 15 ms, mem = 848 KiB, score = 10
测试数据 #1: Accepted, time = 0 ms, mem = 848 KiB, score = 10
测试数据 #2: Accepted, time = 0 ms, mem = 844 KiB, score = 10
测试数据 #3: Accepted, time = 0 ms, mem = 848 KiB, score = 10
测试数据 #4: Accepted, time = 0 ms, mem = 844 KiB, score = 10
测试数据 #5: Accepted, time = 0 ms, mem = 848 KiB, score = 10
测试数据 #6: Accepted, time = 0 ms, mem = 840 KiB, score = 10
测试数据 #7: Accepted, time = 31 ms, mem = 844 KiB, score = 10
测试数据 #8: Accepted, time = 15 ms, mem = 844 KiB, score = 10
测试数据 #9: Accepted, time = 15 ms, mem = 844 KiB, score = 10
Accepted, time = 76 ms, mem = 848 KiB, score = 100

一次AC，考虑了多种情况，通过即可

贪心的方法是：先快排，从大到小，然后选从最大到最小，尽量使2个物品和接近W，然后标记为不可选取，答案+1，继续选取。

program ex;
var data:array[0..30001] of longint;
a,b,c,w,i,j,num,n,ans:longint;

procedure qsort(x,y:longint);
var i,r,mid,l,j,k:longint;
begin
r:=x; l:=y;
mid:=data[(x+y) div 2];

repeat
while data[r]>mid do inc(r);
while data[l]<mid do dec(l);

if r<=l then
begin
k:=data[r];
data[r]:=data[l];
data[l]:=k;
inc(r);
dec(l);
end;
until r>l;

if x<l then qsort(x,l);
if r<y then qsort(r,y);

end;

begin //main
ans:=0;
read(w); read(n);
data[n+1]:=201;
for i:=1 to n do
begin
read(num);
data[i]:=num;
end;

qsort(1,n);

for i:=1 to n do
begin
a:=data[i];

if data[i]=201 then
continue;
if data[i]>w then
begin
data[i]:=201;
continue;
end;

for j:=i+1 to n+1 do
begin
if (a+data[j])<=w then
begin
a:=0;
data[j]:=201;
data[i]:=201;
ans:=ans+1;
break;
end;
if j=n+1 then
begin
a:=0;
data[i]:=201;
ans:=ans+1;
end;

end;
end;
write(ans);
end.

5min水过。
#include<iostream>
#include<cstring>
#include<cmath>
#include<algorithm>
using namespace std;
int pi[30001];
int main()
{
int w,n;
cin>>w>>n;
for(int i=0;i<n;i++)
cin>>pi[i];
sort(pi,pi+n);
int count=0,ans=0;
for(int i=n-1;i>=0;i--)
{
int flag=1;
for(int j=count;j<i;j++)
{
if(pi[i]+pi[j]<=w)
{
ans++;
count++;
flag=0;
break;
}
}
if(flag)
{
ans++;
}
if(i==count)
break;
}
cout<<ans<<endl;
return 0;
}
排序之后大小配对。

var
flag:boolean;
bool:array[1..100000] of boolean;
w,i,j,n,k,temp,tot:longint;
a:array[1..30000] of longint;
procedure qsort(l,r:longint);
var
i,j,k:longint;
begin
i:=l;
j:=r;
k:=(i+j) div 2;
temp:=a[k];
a[k]:=a[l];
while i<j do
begin
while (i<j)and(a[j]>temp) do
dec(j);
if i<j then
begin
a[i]:=a[j];
inc(i);
end;
while (i<j)and(a[i]<temp) do
inc(i);
if i<j then
begin
a[j]:=a[i];
dec(j);
end;
end;
a[i]:=temp;
if i-1>l then
qsort(l,i-1);
if i+1<r then
qsort(i+1,r);
end;

begin
readln(w);
readln(n);
for i:=1 to n do
readln(a[i]);
qsort(1,n);

for i:=1 to n do
if not bool[i] then
begin
flag:=false;
for j:=n downto i+1 do
if (not bool[j])and(a[i]+a[j]<=w) then
begin
bool[i]:=true;
bool[j]:=true;
flag:=true;
inc(tot);
break;
end;
if not flag then
break;
end;
writeln(n-tot);
end.
关于淳朴的贪心

var
a:array[1..200]of longint;
c,w,n,b,i,j,ans:longint;
begin
readln(w);readln(n);for i:=1 to n do begin readln(b);inc(a[b]);end;
for i:=1 to w do
begin
c:=0;
while (a[i]>0)and(a[i]<>c) do
begin
c:=a[i];
for j:=w downto i+1 do while (a[i]>0)and(a[j]>0)and(i+j<=w)do
begin dec(a[i]);dec(a[j]);inc(ans);end;
end;
end;
for i:=1 to w do while (2*i<=w)and(a[i]>=2) do begin dec(a[i],2);inc(ans);end;
writeln(n-ans);
end.

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

int main()
{
int pi[300000], w, n, sum = 0, i, j;
cin >> w;
cin >> n;
for(i = 0; i < n; i++) cin >> pi[i];
sort(pi, pi + n);
for(i = 0, j = n - 1; i <= j;) {
if(pi[i] + pi[j] <= w) {
sum++;

i++;
} else if(pi[j] <= w) {
sum++;
}
j--;
}
if(i == j) sum++;
cout << sum << "\n";

return 0;
}

这是我源码

评测结果

编译成功

测试数据 #0: Accepted, time = 0 ms, mem = 1416 KiB, score = 10

测试数据 #1: Accepted, time = 0 ms, mem = 1412 KiB, score = 10

测试数据 #2: Accepted, time = 0 ms, mem = 1416 KiB, score = 10

测试数据 #3: Accepted, time = 0 ms, mem = 1412 KiB, score = 10

测试数据 #4: Accepted, time = 0 ms, mem = 1416 KiB, score = 10

测试数据 #5: Accepted, time = 46 ms, mem = 1416 KiB, score = 10

测试数据 #6: Accepted, time = 93 ms, mem = 1416 KiB, score = 10

测试数据 #7: Accepted, time = 78 ms, mem = 1412 KiB, score = 10

测试数据 #8: Accepted, time = 93 ms, mem = 1416 KiB, score = 10

测试数据 #9: Accepted, time = 124 ms, mem = 1412 KiB, score = 10

Accepted, time = 434 ms, mem = 1416 KiB, score = 100

运行都对了，但是在soj上却通过不了，是因为vijos的测试数据没有soj好吗，soj是1483题，哪位大神能说明下呢

整理一下，刚才发的不好。
#include<iostream>
#include<algorithm>
using namespace std;
int a[1000001];
int main()
{
int w,n,i,k=0,l,js=0;
cin>>w>>n;
for(i=0;i<=n-1;i++)cin>>a[i];
int j=n-1;
sort(a,a+n);
while(j>=k)
{
while(a[j--]+a[k]>w)js++;
js++,k++;
}
cout<<js<<endl;
return 0;
}

超短20行版！！！
#include<iostream>
#include<algorithm>
using namespace std;
int a[1000001];
int main()
{
int w,n,i,k=0,l,js=0;
cin>>w>>n;
for(i=0;i<=n-1;i++)cin>>a[i];
int j=n-1;
sort(a,a+n);
while(j>=k)
{
while(a[j--]+a[k]>w)js++;
js++,k++;
}
cout<<js<<endl;
return 0;
}

#include<iostream>
#include<cstdio>
#include<cstring>
#include<algorithm>
using namespace std;
int n,m;
int a[30005];
int ans;
int main()
{
cin>>n;
cin>>m;
for(int i=1;i<=m;i++)cin>>a[i];
sort(a+1,a+m+1);
int x=1;int y=m;
while(x!=y)
{
if(a[x]+a[y]>n)
{
ans++;
y--;
}
else
{
x++;y--;ans++;
}
if(x==y){
ans++;break;
}
if(x>y)break;
}
cout<<ans<<endl;
return 0;
}

为什么会超时？？？？？？？？？？？？？？？？？？？？？
BS！！！！！！！！！！！！！！！！！！！

var
gift:array[1..30000] of integer;
maxn,n,i,j,t,s,flag:integer;
begin
readln(maxn);
readln(n);
for i:=1 to n do readln(gift[i]);
for i:=1 to n-1 do
for j:=i+1 to n do
if gift[i]<gift[j] then
begin
t:=gift[i];gift[i]:=gift[j];gift[j]:=t;
end;
for i:=n downto 1 do
begin
flag:=0;
for j:=1 to i-1 do
if (gift[i]+gift[j]<=maxn) and (gift[i]<>-1) and (gift[j]<>-1) then
begin
s:=s+1;
gift[i]:=-1;
gift[j]:=-1;
flag:=1;
break;
end;
if (flag=0) and (gift[i]<>-1) then s:=s+1;
end;
writeln(s);
end.

这道题建议用基数排序，速度最快，时间复杂度最低
评测结果
编译成功

foo.pas(18,11) Warning: Variable "p" does not seem to be initialized
foo.pas(49,17) Warning: Variable "ans" does not seem to be initialized
测试数据 #0: Accepted, time = 15 ms, mem = 940 KiB, score = 10
测试数据 #1: Accepted, time = 0 ms, mem = 944 KiB, score = 10
测试数据 #2: Accepted, time = 0 ms, mem = 944 KiB, score = 10
测试数据 #3: Accepted, time = 0 ms, mem = 940 KiB, score = 10
测试数据 #4: Accepted, time = 0 ms, mem = 944 KiB, score = 10
测试数据 #5: Accepted, time = 15 ms, mem = 944 KiB, score = 10
测试数据 #6: Accepted, time = 140 ms, mem = 944 KiB, score = 10
测试数据 #7: Accepted, time = 140 ms, mem = 944 KiB, score = 10
测试数据 #8: Accepted, time = 296 ms, mem = 944 KiB, score = 10
测试数据 #9: Accepted, time = 359 ms, mem = 940 KiB, score = 10
Accepted, time = 965 ms, mem = 944 KiB, score = 100

程序：
program present;
var w,n,i,j,t,ans,tt:longint;
a:array[0..30000] of longint;
p:array[1..200] of longint;
sweep:boolean;
begin
//assign(input,'present.txt');
//reset(input);
read(w,n);
for i:=1 to n do
read(a[i]);
//close(input);
//assign(input,'');
//reset(input);
tt:=1;
a[0]:=1000;
for i:=1 to n do
inc(p[a[i]]);
for i:=200 downto 1 do
if p[i]>0 then
begin
for j:=tt to tt+p[i]-1 do
a[j]:=i;
tt:=tt+p[i];
end;
for i:=1 to n do
begin
j:=n;
tt:=0;
if a[i]=0 then
continue;
while (a[j]=0) and (j>0) do dec(j);
while a[i]+a[j]<=w do
begin
if i>=j then
break;
if (a[tt]<>a[j]) and (j>0) then
tt:=j;
dec(j);
while (a[j]=0) and (j>0) do dec(j);
if j=0 then
break;
end;
j:=tt;
if j=0 then
j:=i;
if a[i]<>0 then
begin
inc(ans);
a[i]:=0;
a[j]:=0;
end;
end;
writeln(ans);
//readln(ans);
end.

include <cstdlib> include <iostream>

using namespace std;

int main(int argc, char *argv[])
{
int m,s,t,dis,time;
time=0;
dis=0;
cin>>m>>s>>t;
while (1)
{
if (dis>=s)
{
cout<<"Yes"<<endl;
cout<<time;
break;
}
else
{
if (time<t)
{
if (m>=10)
{
m-=10;
time+=1;
dis+=60;
}
else
{
if ((s-dis)>=60 and (t-time)>=((10-m)-(10-m)%4)/4+1+1)
{
m+=4;
time++;
}
else
{
time++;
dis+=17;
}
}
}
else
{
cout<<"No"<<endl;
cout<<dis;
}
}
}

return EXIT_SUCCESS;
}

o(￣▽￣)o 刚才没发现 AC40题纪念！~~~~~

=、= RP不好 WA了三次。。。 原因是代码复制错了--||
Var w,n,i,j,ans,t,tmp,head,tail:longint;
v:array[1..100000] of boolean;
a:array[1..100000] of longint;
Procedure qsort(l,r:longint);
Var i,j,x,y:longint;
Begin
i:=l; j:=r;
x:=a[(l+r) shr 1];
repeat
while x>a[i] do inc(i);
while x<a[j] do dec(j);
if i<=j then
begin
y:=a[i];
a[i]:=a[j];
a[j]:=y;
inc(i); dec(j);
end;
Until i>j;
If i<r then qsort(i,r);
if l<j then qsort(l,j);
End;
Begin
readln(w);
readln(n);
For i:=1 to n do readln(a[i]);
qsort(1,n);
head:=1; tail:=n;
While head<=tail do
Begin
tmp:=a[head]+a[tail];
If tmp<=w then begin inc(ans); inc(head); dec(tail); end;
If tmp>w then
Begin
dec(tail);
inc(ans);
End;
End;
Writeln(ans);
End.