Merge pull request 7oSkaaa#1103 from aboelsooud/main

add the 18'th day problem solution

05- May/18- Minimum Number of Vertices to Reach All Nodes/18- Minimum Number of Vertices to Reach All Nodes (Mahmoud Aboelsoud).cpp

@@ -0,0 +1,26 @@
+// Author: Mahmoud Aboelsoud
+
+class Solution {
+public:
+    vector<int> findSmallestSetOfVertices(int n, vector<vector<int>>& edges) {
+        // to find the minimum number of vertices to reach all nodes we need to find the nodes with zero in degree
+        // because we can reach all nodes from the nodes with zero in degree
+        // we can do that by counting the in degree of each node
+        // then loop over the nodes and add the nodes with zero in degree to the answer
+
+        // in_degree: in_degree[i] -> the in degree of node i
+        // ans: the answer
+        vector<int> in_degree(n), ans;
+
+        // count the in degree of each node
+        for(auto&i: edges) in_degree[i[1]]++;
+
+        // loop over the nodes and add the nodes with zero in degree to the answer
+        for(int i = 0; i < n; i++){
+            if(!in_degree[i]) ans.emplace_back(i);
+        }
+
+        // return the answer
+        return ans;
+    }
+};