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由于該圖不是一顆樹，所以首先要將一些塊壓縮成點，所謂塊就是沒有割點的分量，于是只要求出割邊，然后刪除，之后對整個圖進行Floodfill，得到的連通分量再用割邊 補圖，得到的圖一定是一棵樹，然后就可以樹形DP了。  #include <iostream>
#define MAXN 100010
using namespace std;
  struct list  {
 list *next;
int ID;
 };
int n, m;
int value[ MAXN ];
list data[ 1000000 ];
list *vec[ MAXN ];
list *Bri[ MAXN ];
int Ance[ MAXN ];
int Dep[ MAXN ];
int Color[ MAXN ];
int father[ MAXN ];
bool Cut[ MAXN ];
int num[ MAXN ];
#define G 0 // Grey 正在訪問
#define B 1 // Black 訪問完畢
#define W 2 // White 未曾訪問
int root, T;
/**//*******************求無向圖割邊割點********************
* list vec[i] 表示原的鄰接表 *
* list Bri[i] 保存割邊 *
* bool Cut[i] 保存割點 *
* int Ance[i] 保存和i或i的子孫鄰接的最高輩分的祖先的深度 *
* int Dep[i] 保存i點所在的深度 *
* int Color[i] 保存當前結(jié)點訪問情況 *
* int father[i] 保存i的父親結(jié)點的編號 *
* int num[i] 縮點后每個點所在的新塊的編號 *
*********************************************************/
int Min ( int a, int b ) {
return a < b ? a : b;
}
void BridgeCut( int key, int depth ) {
int son = 0;
Dep[ key ] = depth;
Color[ key ] = G;
Ance[ key ] = depth;
list *p, *q;
  for( p = vec[ key ]->next; p ; p = p->next ) {
int next = p->ID;
if( next != father[ key ] && Color[ next ] == G) {
Ance[ key ] = Min( Ance[ key ], Dep[ next ] );
 }
if( Color[ next ] == W ) {
father[ next ] = key;
BridgeCut( next, depth + 1);
son ++; Ance[ key ] = Min( Ance[ key ], Ance[ next ] );
// 判割點
if( key == root ) {
if( son > 1 ) {
Cut[ key ] = true;
}
}else {
if( Ance[ next ] >= Dep[ key ] ) {
Cut[ key ] = true;
}
}
// 判割邊
if( Ance[ next ] > Dep[ key ] ) {
q = &data[ T++ ];
q->ID = next;
q->next = Bri[ key ]->next;
Bri[ key ]->next = q;
q = &data[ T++ ];
q->ID = key;
q->next = Bri[ next ]->next;
Bri[ next ]->next = q;
}
}
}
Color[ key ] = B;
}
void CreateGraph() {
int i, x, y;
T = 0;
for(i = 1; i <= n; i++)
scanf("%d", &value[i]);
for(i = 1; i <= n; i++) {
Bri[i] = &data[ T++ ];
Bri[i]->ID = i;
Bri[i]->next = NULL;
vec[i] = &data[ T++ ];
vec[i]->ID = i;
vec[i]->next = NULL;
Ance[i] = INT_MAX;
Cut[i] = false;
Color[ i ] = W;
}
list *p;
while( m-- ) {
scanf("%d %d", &x, &y);
p = &data[ T++ ];
p->next = vec[x]->next;
p->ID = y;
vec[x]->next = p;
p = &data[ T++ ];
p->next = vec[y]->next;
p->ID = x;
vec[y]->next = p;
}
}
/**//*
割邊割點輸出，以及縮塊后的圖的鄰接表
*/
void Print() {
list *p;
int i;
for(i = 1; i <= n; i++) {
printf("%d: ", i);
for(p = Bri[i]->next; p; p = p->next) {
printf("%d ", p->ID);
}
puts("");
}
for(i = 1; i <= n; i++) {
if( Cut[i] )
printf("point : %d\n", i);
}
}
/**//*以下是樹形DP的過程*/
bool IsBridge(int u, int v) {
list *p;
for( p = Bri[u]->next; p ; p = p->next ) {
if( p->ID == v )
return 1;
}
return 0;
}
int F;
// 分塊
void dfs( int key ) {
list *p;
num[ key ] = F;
for(p = vec[ key ]->next; p ; p = p->next ) {
if( Color[ p->ID ] == W && !IsBridge(key, p->ID) ) {
Color[ p->ID ] = B;
dfs( p->ID );
}
}
}
void FloodFill() {
int i;
for(i = 1; i <= n; i++)
Color[i] = W;
F = 1;
for(i = 1; i <= n; i++) {
if( Color[i] == W ) {
Color[i] = B;
dfs(i);
F ++;
}
}
}
__int64 AllVal[ MAXN ];
__int64 M, zong;
list *New[ MAXN ];
int hash[ MAXN ];
// TreeDp
void Search( int key ) {
list *p;
int son = 0;
for( p = New[ key ]->next; p; p = p->next) {
int q = p->ID;
if( hash[ q ] )
continue;
son ++;
hash[ q ] = 1;
Search(q);
AllVal[ key ] += (__int64)AllVal[ q ];
__int64 a = zong - AllVal[ q ];
__int64 b = AllVal[ q ];
a -= b;
if( a < 0)
a = -a;
if( a < M )
M = a;
}
}
void TreeDp() {
int i;
M = 0;
memset( AllVal, 0, sizeof(AllVal) );
for(i = 1; i <= n; i++) {
AllVal[ num[i] ] += (__int64)value[i];
M += (__int64)value[i];
}
zong = M;
F --;
for(i = 1; i <= F; i++) {
New[i] = &data[ T++ ];
New[i]->ID = i;
New[i]->next = NULL;
}
list *p, *q;
for(i = 1; i <= n; i++) {
for(p = Bri[i]->next; p; p = p->next) {
q = &data[ T++ ];
q->ID = num[ p->ID ];
q->next = New[ num[i] ]->next;
New[ num[i] ]->next = q;
}
}
memset( hash, 0, sizeof(hash) );
hash[1] = 1;
Search(1);
}
int main() {
int i;
int t = 1;
while( scanf("%d %d", &n, &m) != EOF && (n || m) ) {
CreateGraph();
root = 1;
father[ root ] = 0;
BridgeCut( root, 0 );
FloodFill();
//Print();
TreeDp();
printf("Case %d: %I64d\n", t++, M);
}
return 0;
}
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