leecode，rt_phm更新更新

Leecode/src/main/java/com/markilue/leecode/hot100/second/T64_207_CanFinish.java

@@ -73,7 +73,7 @@ public class T64_207_CanFinish {
     }
 
     boolean valid = true;
-
+    //本质上就是图的深度优先搜索:检测这个图是否存在环路
     public boolean canFinish1(int numCourses, int[][] prerequisites) {
         edge = new ArrayList<>();
         for (int i = 0; i < numCourses; i++) {
@@ -95,6 +95,7 @@ public class T64_207_CanFinish {
         return valid;
     }
 
+    //0表示没遍历过；1表示遍历中；2表示遍历过
     public void dfs(int start, int[] visited) {
         visited[start] = 1;//设置为遍历过了
         List<Integer> childern = edge.get(start);