Leetcode - Minimum Number of Vertices to Reach All Nodes

Author: pri1311

Leetcode Top Interview Questions/README.md

@@ -104,6 +104,7 @@
 - [Populating Next Right Pointers in Each Node](https://leetcode.com/problems/populating-next-right-pointers-in-each-node/) - [Cpp Solution](./solutions/Populating%20Next%20Right%20Pointers%20in%20Each%20Node.cpp)
 - [Kth Smallest Element in a BST](https://leetcode.com/problems/kth-smallest-element-in-a-bst/) - [Cpp Solution](./solutions/Kth%20Smallest%20Element%20in%20a%20BST.cpp)
 - [Number of Islands](https://leetcode.com/problems/number-of-islands/) - [Cpp Solution](./solutions/Number%20of%20Islands.cpp)
+- [Minimum Number of Vertices to Reach All Nodes](https://leetcode.com/problems/minimum-number-of-vertices-to-reach-all-nodes/) - [Cpp Solution](./solutions/Minimum%20numberof%20vertices.cpp)
 
 ### 4. Backtracking
 

Leetcode Top Interview Questions/solutions/Minimum numberof vertices.cpp

@@ -0,0 +1,48 @@
+// 1557. Minimum Number of Vertices to Reach All Nodes
+
+// Given a directed acyclic graph, with n vertices numbered from 0 to n-1, and an array edges where edges[i] = [fromi, toi] represents a directed edge from node fromi to node toi.
+
+// Find the smallest set of vertices from which all nodes in the graph are reachable. It's guaranteed that a unique solution exists.
+
+// Notice that you can return the vertices in any order.
+
+// Example 1:
+
+
+
+// Input: n = 6, edges = [[0,1],[0,2],[2,5],[3,4],[4,2]]
+// Output: [0,3]
+// Explanation: It's not possible to reach all the nodes from a single vertex. From 0 we can reach [0,1,2,5]. From 3 we can reach [3,4,2,5]. So we output [0,3].
+// Example 2:
+
+
+
+// Input: n = 5, edges = [[0,1],[2,1],[3,1],[1,4],[2,4]]
+// Output: [0,2,3]
+// Explanation: Notice that vertices 0, 3 and 2 are not reachable from any other node, so we must include them. Also any of these vertices can reach nodes 1 and 4.
+ 
+
+// Constraints:
+
+// 2 <= n <= 10^5
+// 1 <= edges.length <= min(10^5, n * (n - 1) / 2)
+// edges[i].length == 2
+// 0 <= fromi, toi < n
+// All pairs (fromi, toi) are distinct.
+
+class Solution {
+public:
+    vector<int> findSmallestSetOfVertices(int n, vector<vector<int>>& edges) {
+        vector<int> temp(n, 0);
+        for (int i=0;i<edges.size();i++){
+            temp[edges[i][1]]++;
+        }
+        vector<int>ans;
+        for (int i=0;i<n;i++){
+            if (temp[i]==0){
+                ans.push_back(i);
+            }
+        }
+        return ans;
+    }
+};