ok i'm back: 210-course-schedule-ii, 43-multiply-strings

210-course-schedule-ii/driver.cpp

@@ -0,0 +1,13 @@
+#include "soln.hpp"
+
+int main()
+{
+	int numCourses = 4;
+	vector<vector<int>> prerequisites{{0, 1}, {0, 2}, {3, 0}};
+	Solution soln;
+	cout << "Ordering of courses:" << endl;
+	for (int num : soln.findOrder(numCourses, prerequisites))
+		cout << "->" << num;
+	cout << endl;
+	return 0;
+}

210-course-schedule-ii/soln.cpp

@@ -0,0 +1,43 @@
+#include "soln.hpp"
+
+vector<int> Solution::findOrder(int numCourses, vector<vector<int>> &prerequisites)
+{
+	vector<vector<int>> adj(numCourses); // adjacency list
+	vector<int> ans_order;
+	vector<int> in_degrees(numCourses);
+
+	for (vector<int> &p : prerequisites)
+	{
+		adj[p[1]].push_back(p[0]); // [1,0] -> course 1 will have incoming edge from 0
+		in_degrees[p[0]]++;		   // increment in degree of course 1
+	}
+
+	// find starting nodes, which don't hv prereqs
+	// so this will be 0 alone
+	queue<int> bfs_q;
+	for (int i = 0; i < numCourses; i++)
+	{
+		if (in_degrees[i] == 0)
+			bfs_q.push(i);
+	}
+
+	// BFS
+	while (bfs_q.size())
+	{
+		int cur = bfs_q.front();
+		bfs_q.pop();
+		ans_order.push_back(cur);
+		for (int out_node : adj[cur])
+		{
+			// check if no more prereqs
+			// if yes, bfs on that
+			if (in_degrees[out_node] == 1)
+				bfs_q.push(out_node);
+			in_degrees[out_node]--;
+		}
+	}
+	// if solution exists, answer will have all courses
+	if (ans_order.size() == numCourses)
+		return ans_order;
+	return {};
+}

210-course-schedule-ii/soln.hpp

@@ -0,0 +1,7 @@
+#include <bits/stdc++.h>
+using namespace std;
+class Solution
+{
+public:
+	vector<int> findOrder(int numCourses, vector<vector<int>> &prerequisites);
+};