HDU 2242 考研路茫茫——空调教室

考研路茫茫——空调教室

http://acm.hdu.edu.cn/showproblem.php?pid=2242

分析：

　　树形dp，删边。

代码：

#include<cstdio>
#include<algorithm>
#include<cstring>

using namespace std;

const int MAXN = 10010;
const int MAXM = 50010;

struct Edge{
    int to,nxt;
}e[MAXM];
int head[MAXM],tot;
int son[MAXN],Sum,ans;

inline int read() {
    int x = 0,f = 1;char ch = getchar();
    for (; ch<'0'||ch>'9'; ch = getchar())
        if (ch=='-') f = -1;
    for (; ch>='0'&&ch<='9'; ch = getchar())
        x = x*10+ch-'0';
    return x*f;
}
inline void add_edge(int u,int v) {
    e[++tot].to = v,e[tot].nxt = head[u],head[u] = tot;
}
inline void init() {
    memset(head,0,sizeof(head));
    ans = 1e9; // ans也要初始化！！！ 
    tot = Sum = 0;
}
void dfs(int u,int fa) {
    for (int i=head[u]; i; i=e[i].nxt) {
        int v = e[i].to;
        if (v==fa) continue;
        dfs(v,u);
        son[u] += son[v];
        ans = min(ans,abs(Sum-son[v]-son[v]));
    }
}

int main() { 
    int n,m,CASE = 0;
    while (scanf("%d%d",&n,&m)!=EOF) {
        init();
        for (int i=1; i<=n; ++i) son[i] = read(),Sum += son[i];
        for (int u,v,i=1; i<=m; ++i) {
            u = read(),v = read();
            add_edge(u,v),add_edge(v,u);
        }
        dfs(0,-1);
        printf("Case %d: %d
",++CASE,ans);
    }
    return 0;
}