P3942 将军令 [贪心]

$将军令$

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Description

链接

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Solution

不断从深度最大的节点的$K$级父节点进行扩展

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Attention

注意 扩展 时使用 $DFS$, 因为 $BFS$ 保存上一个经过的节点较麻烦
代码中有$BFS$ 函数, 仅供参考, 由于回环往复地入队, $TLE$ 不可避免,

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Code

#include<bits/stdc++.h>
#define reg register

int read(){
        int s = 0, flag = 1;
        char c;
        while((c=getchar()) && !isdigit(c))
                if(c == '-'){ c = getchar(), flag = -1; break ; }
        while(isdigit(c)) s = s*10 + c-'0', c = getchar();
        return s * flag;
}

const int maxn = 100005;

int N;
int K;
int num0;
int Ans;
int head[maxn];
int Fa[maxn];
int f[maxn], Used[maxn];
std::queue <int> Q;

struct Edge{ int nxt, to; } edge[maxn << 1];

void Add(int from, int to){ edge[++ num0] = (Edge){ head[from], to }; head[from] = num0; }

void BFS(int k){
        while(!Q.empty()) Q.pop();
        Q.push(k); f[k] = K, Used[k] = 1;
        while(!Q.empty()){
                int ft = Q.front(); Q.pop();
                for(reg int i = head[ft]; i; i = edge[i].nxt){
                        int to = edge[i].to;
                        if(Used[to]) continue ;
                        Used[to] = 1;
                        if(f[ft]-1) f[to] = f[ft] - 1, Q.push(to);
                }
        }
}

struct Node{
        int dep, id;
} T[maxn];

void DFS(int k, int fa){
        T[k].id = k;
        Fa[k] = fa;
        T[k].dep = T[fa].dep + 1;
        for(reg int i = head[k]; i; i = edge[i].nxt){
                int to = edge[i].to;
                if(to == fa) continue ;
                DFS(to, k);
        }
}

void DFS_2(int k, int left, int last){
        Used[k] = 1;
        if(!left) return ;
        for(reg int i = head[k]; i; i = edge[i].nxt){
                int to = edge[i].to;
                if(to == last) continue ;
                DFS_2(to, left-1, k);
        }
}

bool cmp(Node a, Node b){ return a.dep < b.dep; }

int main(){
        N = read(), K = read();
        int ____ = read();
        if(!K){ printf("%d
", N); return 0; }
        for(reg int i = 1; i < N; i ++){
                int u = read(), v = read();
                Add(u, v), Add(v, u);
        }
        DFS(1, 0);
        std::sort(T+1, T+N+1, cmp);
        for(reg int i = N; i >= 1; i --){
                int t = T[i].id;
                if(!Used[t]){
                        for(reg int j = 1; j <= K; j ++) 
                                if(Fa[t]) t = Fa[t];
                                else break ;
                        DFS_2(t, K, 0), Ans ++;
                }
        }
        printf("%d
", Ans);
        return 0;
}