1.构建图使用递归和回溯实现最长路径通过100%public class Solution {    public String LongestBehaviorPath (String[] paths) {            Map<String,List<String>> graph = new HashMap<>();        Map<String,Integer> indegree = new HashMap<>();        for(String path : paths){            String []steps = path.split("->");            for(int i = 0;i<steps.length-1;i++){                graph.putIfAbsent(steps[i],new ArrayList<>());                graph.get(steps[i]).add(steps[i+1]);                indegree.put(steps[i+1],indegree.getOrDefault(steps[i+1],0)+1);                indegree.putIfAbsent(steps[i],0);            }        }        List<String> startNodes = new ArrayList<>();        for(String node:indegree.keySet()){            if(indegree.get(node) == 0){                startNodes.add(node);            }        }        List<String> longestPath = new ArrayList<>();        for(String start : startNodes){            dfs(start,new ArrayList<>(),graph,longestPath);        }       return String.join("->",longestPath);     }    private static void dfs(String node,List<String> path,Map<String,List<String>> graph,List<String> longestPath){        path.add(node);        if(path.size()> longestPath.size()){            longestPath.clear();            longestPath.addAll(new ArrayList<>(path));        }        if(graph.containsKey(node)){            for(String neighbor: graph.get(node)){                dfs(neighbor,path,graph,longestPath);            }        }        path.remove(path.size() - 1);    }}2.求逆值对双重for循环遍历比较通过100%