Find all paths with min weights in an undirected graph

Posted 2021-06-25 北叶青藤

You are given a list of edges in a graph with weight. Find all the paths between start node and end node with min weights in the path. 

The edges like (node1, node2, weight)

class Solution {
    int minPathSum = Integer.MAX_VALUE;
    public List<List<Integer>> allShortestPaths(int[][] edges, int start, int end) {
        Map<Integer, Map<Integer, Integer>> graph = buildGraph(edges);
        List<List<Integer>> results = new LinkedList<>();
        Set<Integer> visited = new HashSet<>();
        dfs(start, end, visited, graph, new LinkedList<>(), results, 0);
        return results;
    }
    
    private void dfs(int current, int end, Set<Integer> visited, Map<Integer, Map<Integer, Integer>> graph, List<Integer> path, List<List<Integer>> results, int pathSum) {
        path.add(current);
        if (current == end) {
            if (minPathSum > pathSum) {
                results.clear();
                results.add(new LinkedList<>(path));
                minPathSum = pathSum;
            } else if (pathSum == minPathSum) {
                results.add(new LinkedList<>(path));
            }
            path.remove(path.size() - 1);
            return;
        }
        visited.add(current);
        for (Map.Entry<Integer, Integer> entry : graph.getOrDefault(current, new HashMap<>()).entrySet()) {
            if (!visited.contains(entry.getKey())) {
                dfs(entry.getKey(), end, visited, graph, path, results, pathSum + entry.getValue());
            }
        }
        path.remove(path.size() - 1);
        visited.remove(current);
    }    
    private Map<Integer, Map<Integer, Integer>> buildGraph(int[][] edges) {
        Map<Integer, Map<Integer, Integer>> graph = new HashMap<>();
        for (int[] edge : edges) {
            graph.putIfAbsent(edge[0], new HashMap<>());
            graph.putIfAbsent(edge[1], new HashMap<>());
            graph.get(edge[0]).put(edge[1], edge[2]);
            graph.get(edge[1]).put(edge[0], edge[2]);
        }
        return graph;
    }
}