mallcop is a shit problem

MallCop.java

import java.util.*;
import java.io.*;
import java.lang.*;

public class MallCop {
	private static Graph graph;
	private static int n;
	private static int[] distLeaf;
	private static int[] distStart;
	private static int ans;
	public static void main(String[] args) throws FileNotFoundException {
		for (int i = 1; i <= 20; i++) {
			String filename = "in/" + i + ".in";
			solve(filename);
			System.out.println(ans);
		}
		/*
		solve("mallcop.in");
		for (int i = 0; i < n; i++) {
			System.out.println(i + ": " + distStart[i] + "," + distLeaf[i]);
		}
		System.out.println(ans);
		*/
	}
	
	private static void solve(String filename) throws FileNotFoundException {
		Scanner input = new Scanner(new File(filename));
		n = input.nextInt();
		int k = input.nextInt() - 1;
		graph = new Graph(n);
		distLeaf = new int[n];
		distStart = new int[n];
		for (int i = 1; i < n; i++) {
			int s = input.nextInt();
			int d = input.nextInt();
			s--;
			d--;
			int w = input.nextInt();
//			int w = 1;
			graph.addEdge(s, d, w);
		}
		start(k);
		leaf();
		ans = 0;
		dfs(k, -1);
	}
	
	private static void dfs(int i, int p) {
		if (p != -1 && distLeaf[i] <= distStart[i] && distLeaf[p] > distStart[p]) {
			ans++;
		}
		for (int j = 0; j < graph.adjacencylist[i].size(); j++) {
			if (p != graph.adjacencylist[i].get(j).destination) {
				dfs(graph.adjacencylist[i].get(j).destination, i);
			}
		}
	}
	
	private static void start(int i) {
		boolean[] d = new boolean[n];
		Deque<Integer> s = new ArrayDeque<Integer>();
		s.push(i);
		d[i] = true;
		distStart[i] = 0;
		while (!s.isEmpty()) {
			int j = s.pop();
			boolean leaf = true;
			for (int k = 0; k < graph.adjacencylist[j].size(); k++) {
				Edge e = graph.adjacencylist[j].get(k);
				if (!d[e.destination]) {
					d[e.destination] = true;
					distStart[e.destination] = distStart[j] + e.weight;
					s.push(e.destination);
					leaf = false;
				}
			}
			if (leaf) {
				distLeaf[j] = 0;
			} else {
				distLeaf[j] = n+1;
			}
		}
	}
		
	private static void leaf() {
		boolean[] d = new boolean[n];
		Queue<Integer> q = new ArrayDeque<Integer>();
		for (int i = 0; i < distLeaf.length; i++) {
			if (distLeaf[i] == 0) {
				q.add(i);
				d[i] = true;
			}
		}
		while (!q.isEmpty()) {
			int i = q.remove();
			for (int j = 0; j < graph.adjacencylist[i].size(); j++) {
				Edge e = graph.adjacencylist[i].get(j);
				if (!d[e.destination]) {
					d[e.destination] = true;
					distLeaf[e.destination] = distLeaf[i] + e.weight;
					q.add(e.destination);
				}
			}
		}
	}
	
	static class Edge {
        int source;
        int destination;
        int weight;

        public Edge(int source, int destination, int weight) {
            this.source = source;
            this.destination = destination;
            this.weight = weight;
        }
    }

    static class Graph {
        int vertices;
        LinkedList<Edge> [] adjacencylist;

        Graph(int vertices) {
            this.vertices = vertices;
            adjacencylist = new LinkedList[vertices];
            for (int i = 0; i < vertices ; i++) {
                adjacencylist[i] = new LinkedList<>();
            }
        }

        public void addEdge(int source, int destination, int weight) {
            Edge edge = new Edge(source, destination, weight);
            adjacencylist[source].add(edge);
			Edge edge2 = new Edge(destination, source, weight);
			adjacencylist[destination].add(edge2);
        }
    }
}