/* depth-first traversal 
 * two methods: recursive and non-recursive
 * Graph is stored in an adjacency matrix
 */
#include<stdio.h>
#include<stdlib.h>

#define MAX		10

int sp = 0;//stack pointer
int stack[MAX];

/**********************stack***************************/
void push(int f)
{
	if(sp < MAX)
		stack[sp++] = f;
	else
		printf("error: stack full, can't push %d\n", f);
}

int pop(void)
{
	if(sp > 0)
		return stack[--sp];
	else {
		printf("error: stack empty\n");
		return 0;
	}
}


void buildGraph(int adj[][MAX], int n)
{
	int i, j;
	for(i=0; i<n; i++)
		for(j=0; j<n; j++)
		{
			printf("Enter 1 if there is an edge from %d to %d", i, j);
			scanf("%d", &adj[i][j]);
		}
}

/* depth-first traverse, start from node x by using recursive method*/
void dfs(int x, int visited[], int adj[][MAX], int n)
{
	int j;
	visited[x] = 1;
	printf("visit node %d\n", x);
	for(j=0; j<n; j++)
	{
		if(adj[x][j] == 1 && visited[j] == 0)
		{
			//visited[j] = 1;
			dfs(j, visited, adj, n);
		}
	}
}

/* depth-first traverse, start from node x by using non-recursive method */
/* method: put node visited into stack, and find new node not visited*/
void dfs_stack(int x, int visited[], int adj[][MAX], int n)
{
	int i, j;
	int node;
	int count = 1;
	printf("visit node %d\n", x);
	visited[x] = 1;
	node = x;
	push(x); //开始的节点入栈
	while(count < n) //still has node not visited
	{
	/* 所有被访问的节点依次入栈，只有node当找不到下一个相连的节点时，才使用出栈节点 */
		for(j=0; j<n; j++)
		{
			if(adj[node][j] == 1 && visited[j] == 0)
			{
				visited[j] = 1;
				printf("visit node %d\n", j);
				count++;
				push(j); //push node j
				break;
			}
		}
		if(j == n) //与node相连的节点都已经被访问过，所以需要从stack里取出node的上一个节点，再看该节点是否有相连的节点未被访问
			node = pop();
		else      //找到与node相连并且未被访问的节点，
			node = j;
	}
}

main(void)
{
	int adj[MAX][MAX] = {{0, 1, 1, 0, 1},
	 					 {1, 0, 0, 1, 0},
	 					 {1, 0, 0, 1, 0},
	 					 {0, 1, 1, 0, 0},
	 					 {1, 0, 0, 0, 0}
						};
	
	int n = 5;
	char start_node;
	int visited[MAX];
	memset(visited, 0, MAX*sizeof(int));
	//printf("Enter number of nodes in graph: " );
	//scanf("%d", &n);
	//buildGraph(adj, n);
	
	printf("Depth-first traverse, enter the starting node: ");
	while((start_node = getchar()) != EOF)
	{
		getchar();
	    memset(visited, 0, MAX*sizeof(int));
	    printf("recursive: \n");
		dfs((int)atoi(&start_node), visited, adj, n);
		memset(visited, 0, MAX*sizeof(int));
		printf("non-recursive: \n");
	    sp = 0;//此处也要将栈指针清0
		dfs_stack((int)atoi(&start_node), visited, adj, n);
	}
}