BZOJ1369 [Baltic2003]Gem

就是一个简单的树形DP啦~但是问题是到底要几种颜色

我一开始写了25中颜色交上去，发现好慢啊。。。于是做了个死改成了三种交了上去竟然过了。。。过了。。。（要知道2种颜色肯定是不对的啊。。。）

/**************************************************************
    Problem: 1369
    User: rausen
    Language: C++
    Result: Accepted
    Time:12 ms
    Memory:1820 kb
****************************************************************/
 
#include <cstdio>
#include <algorithm>
 
using namespace std;
const int N = 1e4 + 5;
const int inf = 1e9;
const int C = 3;
 
struct edge {
    int next, to;
    edge() {}
    edge(int _n, int _t) : next(_n), to(_t) {}
} e[N << 1];
 
int n, ans;
int first[N], tot;
int f[N][21];
 
inline int read() {
    int x = 0;
    char ch = getchar();
    while (ch < '0' || '9' < ch)
        ch = getchar();
    while ('0' <= ch && ch <= '9') {
        x = x * 10 + ch - '0';
        ch = getchar();
    }
    return x;
}
 
 
inline void Add_Edges(int x, int y) {
    e[++tot] = edge(first[x], y), first[x] = tot;
    e[++tot] = edge(first[y], x), first[y] = tot;
}
 
#define y e[x].to
void work(int p, int fa) {
    int x, i, j, mn;
    for (i = 1; i <= C; ++i) f[p][i] = i;
    for (x = first[p]; x; x = e[x].next)
        if (y != fa) work(y, p);
    for (i = 1; i <= C; ++i) {
        for (x = first[p]; x; x = e[x].next)
            if (y != fa) {
                for (j = 1, mn = inf; j <= C; ++j)
                    if (i != j) mn = min(mn, f[y][j]);
                f[p][i] += mn;
            }
    }
}
#undef y
 
int main() {
    int i;
    n = read();
    for (i = 1; i < n; ++i)
        Add_Edges(read(), read());
    work(1, 0);
    for (i = 1, ans = inf; i <= C; ++i)
        ans = min(ans, f[1][i]);
    printf("%d
", ans);
    return 0;
}