使用C++找到图中的汇节点的数量

Input : n = 4, m = 2

Edges[] = {{2, 3}, {4, 3}}
Output : 2

#include 
using namespace std;
int main(){
    int n = 4; // number of nodes.
    int m = 2; // number of edges.
    vector> edges = {{2, 3}, {4, 3}}; // the edges going from first to second.
    set s;
    for(int i = 0; i < m; i++){
        s.insert(edges[i].first); // will keep value of
                               // distinct node from which edges are going out.
    }
    cout << n - s.size(); // answer is the total number of nodes - number of non sink nodes.
    return 0;
}

2