• hdu5909-Tree Cutting(树形dp)


    偷偷抄bestcoser上面hnust_zhaozhixuan的代码 = = 因为题解看不懂阿

    #include <cstdio>
    #include <cstring>
    
    typedef long long ll;
    
    using namespace std;
    const int N = 1500;
    const int MOD = 1e9 + 7;
    
    int Scan() {
        int x = 0, f = 1; char ch = getchar();
        while (ch < '0' || ch > '9') { if (ch == '-') f = -1; ch = getchar(); }
        while (ch >= '0' && ch <= '9') { x = (x << 3) + (x << 1) + ch - '0'; ch = getchar(); }
        return x * f;
    }
    
    struct Edge {
        int to, next;
    } edge[N*2];
    int head[N], cntE;
    void addedge(int u, int v) {
        edge[cntE].to = v; edge[cntE].next = head[u]; head[u] = cntE++;
        edge[cntE].to = u; edge[cntE].next = head[v]; head[v] = cntE++;
    }
    int a[N], n, m;
    
    int sz[N];      // sz[u] 记录 根为 u 点 有多少个异或值
    int val[N][N];  // val[u][i] 记录 u 点 第 i 个的异或值都是什么
    int dp[N][N];   // dp[u][i] 记录 根为 u 点 异或值为i的数量
    int vis[N][N];  // vis[i] 记录 i 这个 异或值是否出现过
    int tmp[N];
    
    void add(int &a, int b) {
        a = ((ll)a + b) % MOD;
    }
    
    void dfs(int u, int fa) {
        dp[u][ a[u] ] = 1;
        val[u][ sz[u]++ ] = a[u];
        vis[u][ a[u] ] = true;
        for (int i = head[u]; ~i; i = edge[i].next) {
            int v = edge[i].to;
            if (v == fa) continue;
            dfs(v, u);
            memset(tmp, 0, sizeof(int)*m);
            for (int j = sz[u]-1; j >= 0; --j) {
                for (int k = 0; k < sz[v]; ++k) {
                    int a = val[u][j], b = val[v][k];
                    add(tmp[a^b], (ll)dp[u][a] * dp[v][b] % MOD);
                    if (!vis[u][a^b]) val[u][sz[u]++] = a^b, vis[u][a^b] = true;
                }
            }
            for (int j = 0; j < m; ++j) add(dp[u][j], tmp[j]);
        }
    }
    
    
    void init() {
        memset(head, -1, sizeof(int)*(n+2));
        memset(sz, 0, sizeof(int)*(n+2));
        for (int i = 0; i <= n; ++i)
            memset(dp[i], 0, sizeof(int)*m), memset(vis[i], 0, sizeof(int)*m);
        cntE = 0;
    }
    
    int main()
    {
        //freopen("in.txt", "r", stdin);
        int T = Scan();
        while (T--) {
            n = Scan(), m = Scan();
            init();
            for (int i = 1; i <= n; ++i) a[i] = Scan();
            for (int i = 1; i < n; ++i) addedge(Scan(), Scan());
            dfs(1, 0);
    
            for (int k = 0; k < m; ++k) {
                int ans = 0;
                for (int i = 1; i <= n; ++i) add(ans, dp[i][k]);
                printf("%d%c", ans, k==m-1?'
    ':' ');
            }
    
        }
        return 0;
    }
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  • 原文地址:https://www.cnblogs.com/wenruo/p/5927886.html
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