🎉 #1557. Minimum Number of Vertices to Reach All Nodes

Author: GoogTech

#1557. Minimum Number of Vertices to Reach All Nodes/Solution.java

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+/*
+ * @Author: Goog Tech
+ * @Date: 2020-09-15 16:12:07
+ * @LastEditTime: 2020-09-15 16:12:27
+ * @Description: https://leetcode-cn.com/problems/minimum-number-of-vertices-to-reach-all-nodes/
+ * @FilePath: \leetcode-googtech\#1557. Minimum Number of Vertices to Reach All Nodes\Solution.java
+ * @WebSite: https://algorithm.show/
+ */
+
+class Solution {
+    // 解题思路 : 遍历所有的边,使用集合存储所有有向边的终点,
+    // 集合中的所有节点即为入度不为零的节点,剩下的所有节点即为入度为零,即没有前驱的节点.
+    public List<Integer> findSmallestSetOfVertices(int n, List<List<Integer>> edges) {
+        List<Integer> resultList = new ArrayList<>();
+        Set<Integer> endingSet = new HashSet<>();
+        for(List<Integer> edge : edges) endingSet.add(edge.get(1));
+        for(int i = 0; i < n; i++) {
+            if(!endingSet.contains(i)) {
+                resultList.add(i);
+            }
+        }
+        return resultList;
+    }
+}

#1557. Minimum Number of Vertices to Reach All Nodes/Solution.py

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+'''
+Author: Goog Tech
+Date: 2020-09-15 16:12:13
+LastEditTime: 2020-09-15 16:12:39
+Description: https://leetcode-cn.com/problems/minimum-number-of-vertices-to-reach-all-nodes/
+FilePath: \leetcode-googtech\#1557. Minimum Number of Vertices to Reach All Nodes\Solution.py
+WebSite: https://algorithm.show/
+'''
+
+class Solution(object):
+    # 解题思路 : 遍历所有的边,使用集合存储所有有向边的终点,
+    # 集合中的所有节点即为入度不为零的节点,剩下的所有节点即为入度为零,即没有前驱的节点.
+    def findSmallestSetOfVertices(self, n, edges):
+        """
+        :type n: int
+        :type edges: List[List[int]]
+        :rtype: List[int]
+        """
+        endingSet = set(y for x, y in edges)
+        return [i for i in range(n) if i not in endingSet]