vj p1037题解
这个题怎么说呢，还很能唬人的....
写了个很丑的背包....
不过秒掉了！
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编译通过...
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Accepted 有效得分：100 有效耗时：0ms
题解：
f[i,j]表示前i个数搭建的塔的差为j时的最大高度
v[i,j]为boolean数组，前i个数能否到达j的高度
动态方程：
f[i,j]:=max(f[i-1,j-a[i]]+a[i],f[i,j]);(if v[i-1,j-a[i]])
f[i,j]:=max(f[i-1,j+a[i]],f[i,j]);(if v[i-1,j+a[i]])
f[i,j]:=max(f[i-1,j],f[i,j]);if v[i-1,j+a[i]]
代码如下：
1 var n,all,i,j:longint;
2 t:boolean;
3 s,a:array[0..100]of longint;
4 f:array[boolean,-2100..2100]of longint;
5 v:array[boolean,-2100..2100]of boolean;
6 function max(a,b,c:longint):longint;
7 begin
8 max:=a;
9 if b>max then max:=b;
10 if c>max then max:=c;
11 end;
12 begin
13
14 readln(n);
15 all:=0;
16 s[0]:=0;
17 for i:=1 to n do
18 begin
19 read(a[i]);
20 s[i]:=s[i-1]+a[i];
21 end;
22 fillchar(f,sizeof(f),0);
23 fillchar(v,sizeof(v),0);
24 t:=true;
25 v[false,0]:=true;
26 v[true,0]:=true;
27 for i:=1 to n do
28 begin
29 for j:=-s[i] to s[i] do
30 begin
31 f[t,j]:=0;v[t,j]:=false;
32 if v[not(t),j+a[i]] then
33 begin
34 f[t,j]:=f[not(t),j+a[i]];
35 v[t,j]:=true;
36 end;
37 if (v[not(t),j-a[i]])and(f[not(t),j-a[i]]+a[i]>=f[t,j]) then
38 begin
39 f[t,j]:=f[not(t),j-a[i]]+a[i];
40 v[t,j]:=true;
41 end;
42 if (v[not(t),j])and(f[not(t),j]>=f[t,j]) then
43 begin
44 f[t,j]:=f[not(t),j];
45 v[t,j]:=true;
46 end;
47 // write(j,':',f[t,j],' ');
48 end;
49 // writeln;
50 t:=not(t);
51 end;
52 if v[true,0] and v[false,0] then
53 begin
54 if f[true,0]>f[false,0] then
55 begin
56 if f[true,0]=0 then writeln('Impossible') else writeln(f[true,0]);
57 end
58 else
59 begin
60 if f[false,0]=0 then writeln('Impossible')
61 else writeln(f[false,0]);
62 end;
63 end
64 else
65 if (v[true,0])and(f[true,0]<>0) then writeln(f[true,0])
66 else
67 if (v[false,0])and(f[true,0]<>0) then writeln(f[false,0])
68 else
69 writeln('Impossible');
70 end.
2 t:boolean;
3 s,a:array[0..100]of longint;
4 f:array[boolean,-2100..2100]of longint;
5 v:array[boolean,-2100..2100]of boolean;
6 function max(a,b,c:longint):longint;
7 begin
8 max:=a;
9 if b>max then max:=b;
10 if c>max then max:=c;
11 end;
12 begin
13
14 readln(n);
15 all:=0;
16 s[0]:=0;
17 for i:=1 to n do
18 begin
19 read(a[i]);
20 s[i]:=s[i-1]+a[i];
21 end;
22 fillchar(f,sizeof(f),0);
23 fillchar(v,sizeof(v),0);
24 t:=true;
25 v[false,0]:=true;
26 v[true,0]:=true;
27 for i:=1 to n do
28 begin
29 for j:=-s[i] to s[i] do
30 begin
31 f[t,j]:=0;v[t,j]:=false;
32 if v[not(t),j+a[i]] then
33 begin
34 f[t,j]:=f[not(t),j+a[i]];
35 v[t,j]:=true;
36 end;
37 if (v[not(t),j-a[i]])and(f[not(t),j-a[i]]+a[i]>=f[t,j]) then
38 begin
39 f[t,j]:=f[not(t),j-a[i]]+a[i];
40 v[t,j]:=true;
41 end;
42 if (v[not(t),j])and(f[not(t),j]>=f[t,j]) then
43 begin
44 f[t,j]:=f[not(t),j];
45 v[t,j]:=true;
46 end;
47 // write(j,':',f[t,j],' ');
48 end;
49 // writeln;
50 t:=not(t);
51 end;
52 if v[true,0] and v[false,0] then
53 begin
54 if f[true,0]>f[false,0] then
55 begin
56 if f[true,0]=0 then writeln('Impossible') else writeln(f[true,0]);
57 end
58 else
59 begin
60 if f[false,0]=0 then writeln('Impossible')
61 else writeln(f[false,0]);
62 end;
63 end
64 else
65 if (v[true,0])and(f[true,0]<>0) then writeln(f[true,0])
66 else
67 if (v[false,0])and(f[true,0]<>0) then writeln(f[false,0])
68 else
69 writeln('Impossible');
70 end.
