Task: Tarjan
C: #include <stddef.h>
#include <stdlib.h>
#include <stdbool.h>

#ifndef min
#define min(x, y) ((x)<(y) ? (x) : (y))
#endif

struct edge {
	void *from;
	void *to;
};

struct components {
	int nnodes;
	void **nodes;
	struct components *next;
};

struct node {
	int index;
	int lowlink;
	bool onStack;
	void *data;
};

struct tjstate {
	int index;
	int sp;
	int nedges;
	struct edge *edges;
	struct node **stack;
	struct components *head;
	struct components *tail;
};

static int nodecmp(const void *l, const void *r)
{
	return (ptrdiff_t)l -(ptrdiff_t)((struct node *)r)->data;
}

static int strongconnect(struct node *v, struct tjstate *tj)
{
	struct node *w;

	
	v->index = tj->index;
	v->lowlink = tj->index;
	tj->index++;
	tj->stack[tj->sp] = v;
	tj->sp++;
	v->onStack = true;

	for (int i = 0; i<tj->nedges; i++) {
		
		if (tj->edges[i].from != v) {
			continue;
		}
		w = tj->edges[i].to;
		
		if (w->index == -1) {
			int r = strongconnect(w, tj);
			if (r != 0)
				return r;
			v->lowlink = min(v->lowlink, w->lowlink);
		
		} else if (w->onStack) {
			v->lowlink = min(v->lowlink, w->index);
		}
	}

	
	if (v->lowlink == v->index) {
		struct components *ng = malloc(sizeof(struct components));
		if (ng == NULL) {
			return 2;
		}
		if (tj->tail == NULL) {
			tj->head = ng;
		} else {
			tj->tail->next = ng;
		}
		tj->tail = ng;
		ng->next = NULL;
		ng->nnodes = 0;
		do {
			tj->sp--;
			w = tj->stack[tj->sp];
			w->onStack = false;
			ng->nnodes++;
		} while (w != v);
		ng->nodes = malloc(ng->nnodes*sizeof(void *));
		if (ng == NULL) {
			return 2;
		}
		for (int i = 0; i<ng->nnodes; i++) {
			ng->nodes[i] = tj->stack[tj->sp+i]->data;
		}
	}
	return 0;
}

static int ptrcmp(const void *l, const void *r)
{
	return (ptrdiff_t)((struct node *)l)->data
		- (ptrdiff_t)((struct node *)r)->data;
}


struct components *tarjans(
		int nnodes, void *nodedata[],
		int nedges, struct edge *edgedata[],
		int *error)
{
	struct node nodes[nnodes];
	struct edge edges[nedges];
	struct node *stack[nnodes];
	struct node *from, *to;
	struct tjstate tj = {0, 0, nedges, edges, stack, NULL, .tail=NULL};

	
	for (int i = 0; i<nnodes; i++) {
		nodes[i] = (struct node){-1, -1, false, nodedata[i]};
	}
	qsort(nodes, nnodes, sizeof(struct node), ptrcmp);

	
	for (int i = 0; i<nedges; i++) {
		from = bsearch(edgedata[i]->from, nodes, nnodes,
			sizeof(struct node), nodecmp);
		if (from == NULL) {
			*error = 1;
			return NULL;
		}
		to = bsearch(edgedata[i]->to, nodes, nnodes,
			sizeof(struct node), nodecmp);
		if (to == NULL) {
			*error = 1;
			return NULL;
		}
		edges[i] = (struct edge){.from=from, .to=to};
	}

	
	for (int i = 0; i < nnodes; i++) {
		if (nodes[i].index == -1) {
			*error = strongconnect(&nodes[i], &tj);
			if (*error != 0)
				return NULL;
		}
	}
	return tj.head;
}

C#: using System;
using System.Collections.Generic;

class Node
{
    public int LowLink { get; set; }
    public int Index { get; set; }
    public int N { get; }

    public Node(int n)
    {
        N = n;
        Index = -1;
        LowLink = 0;
    }
}

class Graph
{
    public HashSet<Node> V { get; }
    public Dictionary<Node, HashSet<Node>> Adj { get; }

    
    
    
    public void Tarjan()
    {
        var index = 0; 
        var S = new Stack<Node>();

        Action<Node> StrongConnect = null;
        StrongConnect = (v) =>
        {
            
            v.Index = index;
            v.LowLink = index;

            index++;
            S.Push(v);

            
            foreach (var w in Adj[v])
                if (w.Index < 0)
                {
                    
                    StrongConnect(w);
                    v.LowLink = Math.Min(v.LowLink, w.LowLink);
                }
                else if (S.Contains(w))
                    
                    v.LowLink = Math.Min(v.LowLink, w.Index);

            
            if (v.LowLink == v.Index)
            {
                Console.Write("SCC: ");

                Node w;
                do
                {
                    w = S.Pop();
                    Console.Write(w.N + " ");
                } while (w != v);

                Console.WriteLine();
            }
        };

        foreach (var v in V)
            if (v.Index < 0)
                StrongConnect(v);
    }
}