Codeforces 486D Valid Sets tree dp + count

Codeforces 486D Valid Sets tree dp + count

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Given constants d and n, it indicates the tree of n vertices. Each vertex has a certain weight.

Q: How many set of points can be reached by point pairs in a vertex set and the maximum vertex weight is the minimum vertex weight <= d

Ideas:

For each vertex, calculate the number of points that contain this vertex and this vertex is used as the minimum vertex weight in the vertex set, and enumerate each vertex.

import java.io.PrintWriter;import java.text.DecimalFormat;import java.util.ArrayDeque;import java.util.ArrayList;import java.util.Arrays;import java.util.Collections;import java.util.Comparator;import java.util.Deque;import java.util.HashMap;import java.util.Iterator;import java.util.LinkedList;import java.util.Map;import java.util.PriorityQueue;import java.util.Scanner;import java.util.Stack;import java.util.TreeMap;import java.util.TreeSet;import java.util.Queue;public class Main {int n, d;int[] a = new int[N];int ad(int x, int y){x += y;if(x>=mod)x %= mod;return x;}int mul(int x, int y){long xx = (long)x*(long)y;if(xx>=mod) xx %= mod;return (int)xx;}int dfs(int u, int fa, int dep){int ans = 1;for(int i = head[u]; i!=-1; i = edge[i].nex){int v = edge[i].to;if((v == fa)||(a[v]>a[dep]||(a[v]==a[dep]&&v>dep))||(a[dep]-a[v]>d))continue;ans = mul(ans, dfs(v, u, dep)+1);}return ans;}void input(){d = cin.nextInt(); n = cin.nextInt();for(int i = 1; i <= n; i++)a[i] = cin.nextInt();init_edge();for(int i = 1, u, v; i < n; i++){u = cin.nextInt(); v = cin.nextInt();add(u, v); add(v, u);}}void work(){input();int ans = 0;for(int i = 1; i <= n; i++)ans = ad(ans, dfs(i, i, i));out.println(ans%mod);}Main() {cin = new Scanner(System.in);out = new PrintWriter(System.out);}public static void main(String[] args) {Main e = new Main();e.work();out.close(); }public Scanner cin;public static PrintWriter out;static int N = 2005;static int M = 2005;DecimalFormat df=new DecimalFormat("0.0000");static int inf = (int) 1e9 + 7;static long inf64 = (long) 1e18;static double eps = 1e-8;static double Pi = Math.PI;static int mod = 1000000007 ;class Edge{int from, to, nex;Edge(){}Edge(int from, int to, int nex){this.from = from;this.to = to;this.nex = nex;}}Edge[] edge = new Edge[M<<1];int[] head = new int[N];int edgenum;void init_edge(){for(int i = 0; i < N; i++)head[i] = -1; edgenum = 0;}void add(int u, int v){edge[edgenum] = new Edge(u, v, head[u]);head[u] = edgenum++;}int Pow(int x, int y) {int ans = 1;while (y > 0) {if ((y & 1) > 0)ans *= x;y >>= 1;x = x * x;}return ans;}double Pow(double x, int y) {double ans = 1;while (y > 0) {if ((y & 1) > 0)ans *= x;y >>= 1;x = x * x;}return ans;}int Pow_Mod(int x, int y, int mod) {int ans = 1;while (y > 0) {if ((y & 1) > 0)ans *= x;ans %= mod;y >>= 1;x = x * x;x %= mod;}return ans;}long Pow(long x, long y) {long ans = 1;while (y > 0) {if ((y & 1) > 0)ans *= x;y >>= 1;x = x * x;}return ans;}long Pow_Mod(long x, long y, long mod) {long ans = 1;while (y > 0) {if ((y & 1) > 0)ans *= x;ans %= mod;y >>= 1;x = x * x;x %= mod;}return ans;}int gcd(int x, int y){if(x>y){int tmp = x; x = y; y = tmp;}while(x>0){y %= x;int tmp = x; x = y; y = tmp;}return y;}int max(int x, int y) {return x > y ? x : y;}int min(int x, int y) {return x < y ? x : y;}double max(double x, double y) {return x > y ? x : y;}double min(double x, double y) {return x < y ? x : y;}long max(long x, long y) {return x > y ? x : y;}long min(long x, long y) {return x < y ? x : y;}int abs(int x) {return x > 0 ? x : -x;}double abs(double x) {return x > 0 ? x : -x;}long abs(long x) {return x > 0 ? x : -x;}boolean zero(double x) {return abs(x) < eps;}double sin(double x){return Math.sin(x);}double cos(double x){return Math.cos(x);}double tan(double x){return Math.tan(x);}double sqrt(double x){return Math.sqrt(x);}}