Minimum numberof vertices.cpp

// 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;
    }
};