Saturday, May 25, 2024

# Codeforces Round #382 (Div. 2), problem: (E) Ostap and Tree, Accepted Solution in C/C++

```#include <stdio.h>
#include <string.h>
#include <stdlib.h>

#define M	1000000007

int add(int a, int b) { return (a + b) % M; }
int mult(int a, int b) { return ((long long) a * b) % M; }

#define K	20

struct edge {
int v;
struct edge *next;
};

struct vertex {
struct edge *list;
int dp[K + 1][K + 2];
} *vv;

int max(int a, int b, int k) {
return a != k + 1 && b != k + 1 ? (a > b ? a : b) : (a == k + 1 ? b : a);
}

void edgeadd(int u, int v) {
struct edge *x = malloc(sizeof(*x));

x->v = v;
x->next = vv[u].list;
vv[u].list = x;
}

void dfs(int u, int v, int n, int k) {
int i, j, wi, wj, dp[K + 1][K + 2];
struct edge *x;

for (x = vv[v].list; x != NULL; x = x->next)
if (x->v != u)
dfs(v, x->v, n, k);
vv[v].dp[0][k + 1] = vv[v].dp[k][0] = 1; /* the jth node */
for (x = vv[v].list; x != NULL; x = x->next) { /* the tree */
int w = x->v;

memset(dp, 0, (K + 1) * (K + 2) * sizeof(**dp));
if (w != u) {
for (i = 0; i <= k; i++)
for (j = 0; j <= k + 1; j++)
if (vv[v].dp[i][j] != 0)
for (wi = 0; wi <= k; wi++)
for (wj = 0; wj <= k + 1; wj++)
if (vv[w].dp[wi][wj] != 0) {
int i_ = i < wi + 1 ? i : wi + 1;
int j_ = k + 1;

if (j != k + 1 && j + wi + 1 > k)
j_ = max(j_, j, k);
if (wj != k + 1 && wj + 1 + i > k)
j_ = max(j_, wj + 1, k);
if (j_ == k)
continue;
}
memcpy(vv[v].dp, dp, sizeof(**dp) * (K + 1) * (K + 2));
}
}
}

int main() {
int i, n, k, cnt;

scanf("%d%d", &n, &k);
vv = calloc(n, sizeof(*vv));
if (k == 0)
printf("1\n");
else {
for (i = 1; i < n; i++) {
int u, v;

scanf("%d%d", &u, &v);
u--, v--;
}
dfs(-1, 0, n, k);
cnt = 0;
for (i = 0; i <= k; i++)
cnt = add(cnt, vv[0].dp[i][k + 1]);
printf("%d\n", cnt);
}
return 0;
}```

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