Noip Eve: Codevs, pruning flowers

Pruning flowers

time limit: 1 sspace limit: 256000 KBTitle Description Description

ZZ is interested in mathematics, and is a studious student, always stay in the classroom after class to ask the teacher some questions.

One day he rode to class in the morning, on the way to see an old man is pruning flowers and grass, suddenly think of a question about pruning flowers.

Then the day after the lesson, ZZ asked the teacher the question:

A strange flower, with a total of n flowers on it, and a total of N-1 branches to connect the flowers together, and without trimming every

Flowers are not isolated.

Each flower has a "beautiful index", the larger the number indicates that the more beautiful flower, there are "beautiful index" is negative,

This flower is disgusting to look at.

The so-called "pruning", meaning: remove one of the branches, so that a flower has become two strains, throw away one of the strains.

After a series of "pruning", the last flower (or perhaps one) remains.

The teacher's task is to make the remaining strain (which is not done by a series of "trims")

Flower) flowers on the "Beauty Index" and the largest.

The teacher thought for a while, gave the positive solution (the teacher of the big school is very cow ~). ZZ See the problem is easily broken, quite uncomfortable,

So I asked you again.

Enter a description Input Description

The first line is an integer N (1≤n≤16000). A total of n flowers on the original plant flower.

The second line has n integers, and the first integer represents the beautiful exponent of the I flower.

The next N-1 line is two integers A/b, indicating the presence of a branch of a flower and a B flower.

Output description Output Description

A number that represents the maximum value of the sum of the "beautiful exponents" that can be obtained after a series of "trims". Guaranteed absolute value not exceeding

Over 2147483647.

Sample input Sample Input

7

-1-1-1 1 1 1 0

1 4

2 5

3 6

6 U

5 7

6 7

Sample output Sample Output 3

Data range and Tips

Data Size & Hint

Data range:
For 60% of data, ensure n≤1,000
For 100% of data, ensure n≤16,000


Tree-shaped DP
F[i]:=sigma (Max (0,f[son[i])) +init[i]
Code

Type Rec=record x,y:longint;    End;var N:longint;    I,j,k:longint;    Max:longint;    Init:array[1..16000]of Longint;    Edge:array[1..32000]of Rec;    Num1,num2:array[1..16000]of Longint;    Used:array[1..16000]of Boolean;    F:array[1..16000]of Longint;    Num:longint;          X,y:longint;procedure qsort (X,y:longint);              var head,tail,k:longint;          Temp:rec; Begin Head:=x;                Tail:=y;                k:=edge[(head+tail) div 2].x;                            While Head<tail does begin while Edge[head].x<k do Inc (head);                            While k<edge[tail].x do Dec (tail);                                          If Head<=tail then begin Temp:=edge[head];                                          Edge[head]:=edge[tail];                                          Edge[tail]:=temp;                                          Inc (head);                                    Dec (tail);End                End                If Head<y then Qsort (head,y);          If X<tail then Qsort (x,tail);          End;procedure DFS (X:longint);              var i,j,k:longint;          Xxx:longint;                Begin F[X]:=INIT[X];                xxx:=0; For I:=1 to Num2[x] does if USED[EDGE[NUM1[X]+I-1].Y] then begin k:=edge[num1[x]+i-                                  1].Y;                                  Used[k]:=false;                                  Inc (XXX);                                  DFS (k);                            If F[k]>0 then f[x]:=f[x]+f[k];                End                                 if (xxx=0) then BEGIN if (init[x]<0) then f[x]:=0                        else f[x]:=init[x];          End      End;begin READLN (n);      num:=0;      For I:=1 to n do read (Init[i]);     For I:=1 to N-1 do     Begin Inc (NUM);                READLN (x, y);                Edge[num].x:=x;                Edge[num].y:=y;                Inc. (NUM);                Edge[num].x:=y;          Edge[num].y:=x;      End      Qsort (1,num);      Fillchar (Num1,sizeof (NUM1), 0);      Fillchar (Num2,sizeof (num2), 0);      For I:=1 to n do num1[i]:=maxlongint;                For I:=num Downto 1 do BEGIN Inc (num2[edge[i].x]);          If Num1[edge[i].x]>i then num1[edge[i].x]:=i;      End      Fillchar (used,sizeof (used), true);      Fillchar (F,sizeof (f), 0);      Used[i]:=false;      DFS (i);      MAX:=F[1];      For i:=2 to N does if max<f[i] then max:=f[i]; Writeln (max); end.

Noip Eve: Codevs, trimming flowers