BZOJ 1304: [CQOI2009]叶子的染色 树形DP + 结论

Code: 

#include<bits/stdc++.h>
#define setIO(s) freopen(s".in","r",stdin)
#define maxn 1000000 
#define inf 1000000000 
using namespace std; 
int n,m,edges; 
int col[maxn],f[maxn][2],hd[maxn],to[maxn<<1],nex[maxn<<1];
void addedge(int u,int v) 
{
    nex[++edges]=hd[u],hd[u]=edges,to[edges]=v; 
}
void dfs(int u,int ff)
{ 
    if(u<=n) return;  
    for(int i=hd[u];i;i=nex[i])
    {
        int v=to[i]; 
        if(v==ff) continue; 
        dfs(v, u); 
        f[u][0]+=min(f[v][0]-1,f[v][1]); 
        f[u][1]+=min(f[v][1]-1,f[v][0]); 
    }
} 
int main()
{ 
    // setIO("input"); 
    int i,j; 
    scanf("%d%d",&m,&n); 
    for(i=1;i<=m;++i) f[i][0]=f[i][1]=1;             
    for(i=1;i<=n;++i) scanf("%d",&col[i]), f[i][col[i]^1]=inf;  
    for(i=1;i<m;++i) 
    {
        int a,b; 
        scanf("%d%d",&a,&b); 
        addedge(a,b), addedge(b,a);
    }  
    dfs(n+1,0); 
    printf("%d\n",min(f[n+1][0], f[n+1][1])); 
    return 0; 
}