URAL 1022. Genealogical tree

Problem url: http://acm.timus.ru/problem.aspx?space=1&num=1022

This is a typical problem that uses topological sorting. At first I misunderstood it as a normal internal sorting issue and got wrong through sort tree. Later through some hints, I got AC via topo sort algorithm. Here are two AC programs(use different format of topo sorting). In both cases, I use Adjacdent Matrix to represent the Directed Acycline Graph

** using Depth-First Traverse

/* time:0.001s
memory: 267 KB

using Adjacent Matrix to perform topological sort against a directed acycline graph(through depth first search)

*/

#include <cstdio>
#include <iostream>

#define MAXID 100 //max vertex number

using namespace std;

bool g_gene[MAXID+1][MAXID+1]; //Matrix of the graph
bool visited[MAXID+1]; //array used to record whether vertex has been visited
int stack[MAXID]; // used as stack

int N =0; //number of martians

int stop = 0; //top of stack

//Depth First Search against a Graph from the given vertex
void DFS(int id)
{
int j= 0;

visited[id] = true;

for(j=1;j<=MAXID;++j)
{
if(g_gene[id][j] && !visited[j]) DFS(j);
}

//push the current vertext into stack
stack[stop++] = id;
}

void main()
{
int i = 0;
int curkid = 0;

memset(g_gene, 0, sizeof(bool)* (MAXID+1) * (MAXID+1));
memset(visited, 0, sizeof(bool) * (MAXID+1));

scanf("%d", &N);

for(i=1;i<=N;++i)
{

do
{
scanf("%d", &curkid);

if(curkid != 0)
{
g_gene[i][curkid] = 1;
}

}while(curkid != 0);
}

stop = 0;

for(i=1;i<=N;++i)
{
if(!visited[i]) DFS(i);
}

//print out the pushed nodes reversely
for(i=N-1;i>=0;--i)
{
printf("%d ", stack[i]);
}

}

** use Standard Topo Sort approach:

/* time:0.001s
memory: 267 KB

using Adjacent Matrix to perform topological sort against a directed acycline graph(through standard topo sort)

*/

#include <cstdio>
#include <iostream>

#define MAXID 100 //max vertex number

using namespace std;

bool g_gene[MAXID+1][MAXID+1]; //Matrix of the graph
int indegree[MAXID+1]; //store the in-degree of each vertex

int stack[MAXID]; // used as stack

int N =0; //number of martians

int stop = 0; //top of stack

void main()
{
int i = 0;
int j = 0;
int curkid = 0;

memset(g_gene, 0, sizeof(bool)* (MAXID+1) * (MAXID+1));
memset(indegree,0, sizeof(int)* (MAXID+1));

scanf("%d", &N);

for(i=1;i<=N;++i)
{

do
{
scanf("%d", &curkid);

if(curkid != 0)
{
g_gene[i][curkid] = true;
indegree[curkid]++;
}

}while(curkid != 0);
}

stop = 0;

for(i=1;i<=N;++i)
{
if(indegree[i]==0) stack[stop++] = i;
}

//topo sort

while(stop > 0)
{
i = stack[--stop];

printf("%d ", i);

for(j=1;j<=N;++j)
{
if(g_gene[i][j])
{
--indegree[j];

if(indegree[j] == 0) stack[stop++] = j;
}
}

}

}