Poj--3140（Dfs，枚举树边）

2014-12-09 21:35:31

思路：Dfs一遍，找树大小，然后在过程中找答案即可。

　　注意：最大值以后可以以-1设为第一个元素前的标记，以防止题目卡INF！

 1 /*************************************************************************
 2     > File Name: 3140.cpp
 3     > Author: Natureal
 4     > Mail: 564374850@qq.com 
 5     > Created Time: Tue 09 Dec 2014 12:30:04 PM CST
 6 ************************************************************************/
 7 
 8 #include <cstdio>
 9 #include <cstring>
10 #include <cstdlib>
11 #include <cmath>
12 #include <vector>
13 #include <map>
14 #include <set>
15 #include <stack>
16 #include <queue>
17 #include <iostream>
18 #include <algorithm>
19 using namespace std;
20 #define lp (p << 1)
21 #define rp (p << 1|1)
22 #define getmid(l,r) (l + (r - l) / 2)
23 #define MP(a,b) make_pair(a,b)
24 typedef long long ll;
25 const int maxn = 100010;
26 const int Maxn = 1000010;
27 
28 int N,M;
29 ll num[maxn],ans,sum;
30 int first[maxn],next[Maxn],ver[Maxn],ecnt;
31 
32 void Init(){
33     memset(first,-1,sizeof(first));
34     ecnt = 0;
35     sum = 0;
36 }
37 
38 void Add_edge(int u,int v){
39     next[++ecnt] = first[u];
40     ver[ecnt] = v;
41     first[u] = ecnt;
42 }
43 
44 ll Solve(int p,int fa){
45     ll sz = num[p];
46     for(int i = first[p]; i != -1; i = next[i]){
47         int v = ver[i];
48         if(v == fa)
49             continue;
50         ll tmp = Solve(v,p);
51         ll res = sum - tmp - tmp;
52         if(res < 0) res = -res;
53         if(ans == -1) ans = res;
54         else ans = min(ans,res);
55         sz += tmp;
56     }
57     return sz;
58 }
59 
60 int main(){
61     int a,b,Case = 0;
62     while(scanf("%d%d",&N,&M) != EOF){
63         if(N == 0 && M == 0)
64             break;
65         Init();
66         for(int i = 1; i <= N; ++i){
67             scanf("%I64d",&num[i]);
68             sum += num[i];
69         }
70         for(int i = 1; i <= M; ++i){
71             scanf("%d%d",&a,&b);
72             Add_edge(a,b);
73             Add_edge(b,a);
74         }
75         ans = -1;
76         Solve(1,0);
77         printf("Case %d: %I64d\n",++Case,ans);
78     }
79     return 0;
80 }

 

posted @ 2014-12-09 21:36  Naturain  阅读(150)  评论(0)  编辑  收藏  举报