LeetCode - Algorithms - 815. Bus Routes

Hard problem. Accepted after four submissions. Done by myself.

Problem

815. Bus Routes

Java

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class Solution {
    public boolean routesIntersect(int[] route1, int[] route2) {
        boolean r = false;
        Set<Integer> tmpSet = new HashSet<Integer>();
        for(int i=0; i<route1.length; i++)
            tmpSet.add(route1[i]);
        for(int i=0; i<route2.length; i++) {
            if (tmpSet.contains(route2[i])) {
                r = true;
                break;
            }
        }
        return r;
    }

    public boolean inArray(int[] a, int x) {
        boolean b = false;
        for(int i=0; i<a.length; i++) {
            if (x==a[i]) {
                b = true;
                break;
            }
        }
        return b;
    }
    
    public int numBusesToDestination(int[][] routes, int S, int T) {
        if (S==T) return 0;
        int minDist = Integer.MAX_VALUE;

        int h = routes.length;

        List<Integer> list_S = new ArrayList<Integer>();
        for (int i = 0; i < h; i++) {
            for (int j = 0; j < routes[i].length; j++) {
                if (routes[i][j]==S) {
                    list_S.add(i);
                }
            }
        }

        Map<Integer, List<Integer>> reachableRouteMap = new HashMap<Integer, List<Integer>>();
        for(int i=0; i<h; i++) {
            List<Integer> list = new ArrayList<Integer>();
            for(int j=0; j<h; j++) {
                if (j!=i && routesIntersect(routes[i],routes[j])) {
                    list.add(j);
                }
            }
            reachableRouteMap.put(i,list);
        }

        boolean[] visited = new boolean[h];
        for (int i = 0; i < h; i++) {
            visited[i] = false;
        }

        Queue<Node> q = new LinkedList<>();
        for(Integer i : list_S) {
            Node s = new Node(i, 1);
            q.add(s);
        }

        while (!q.isEmpty()) {
            Node curr = q.poll();
            visited[curr.route] = true;
            if (inArray(routes[curr.route], T)) {
                return curr.dist;
            }
            List<Integer> list = reachableRouteMap.get(curr.route);
            for(Integer idx : list) {
                if (visited[idx]==false) {
                    Node node = new Node(idx, curr.dist+1);
                    q.add(node);
                }
            }
        }

        if (minDist == Integer.MAX_VALUE)
            minDist = -1;
        return minDist;        
    }
    
    class Node {
        int route;
        int dist;

        public Node(int route, int dist) {
            this.route = route;
            this.dist = dist;
        }
    }    
}

Submission Detail

  • 45 / 45 test cases passed.
  • Runtime: 1156 ms, faster than 5.02% of Java online submissions for Bus Routes.
  • Memory Usage: 48.2 MB, less than 100.00% of Java online submissions for Bus Routes.