C :

#include<stdio.h>
#include<string.h>

int map[21][21] = {0}, vis[21] = {0}, n, flag = 0, m;
void dfs(int start, int num)
{
	int i;	
	if( num == n - 1 && start == n)
		flag=1;
	if(flag==1)
		return;
	for(i=2;i<=n;++i)
		if(vis[i]!=1&&map[start][i]!=0){
			vis[i]=1;
			dfs(i,num+1);
			vis[i]=0;
		}

}

int main()
{
	
	while(scanf("%d%d", &n, &m) != EOF)
	{
		int i, j;
		memset(map, 0, sizeof(map));
		memset(vis, 0, sizeof(vis));
		for( i = 0; i < 21; i++)
		{
			vis[i] = 0;
			for( j = 0; j < 21; j++)
				map[i][j] = 0;
		}
		flag = 0;
		while(m--)
		{
			int a, b;
			scanf("%d%d", &a, &b);
			map[a][b] = 1;
			map[b][a] = 1;
		}
		dfs(1, 0);
		if(flag)
			printf("1\n");
		else
			printf("0\n");
	}
	return 0;
	
}
	

C++ :

#include <cstdio>
#include <vector>
using namespace std;

int ed, n;
vector < vector < int > > v;

bool dfs(int x, int s) {
    if (s == ed)
        return x == n - 1;
    for (vector < int >::iterator it = v[x].begin(); it != v[x].end(); ++it)
        if (~s >> *it & 1)
            if (dfs(*it, s | (1 << *it)))
                return true;
    return false;
}

int main() {
    int m;
    while (EOF != scanf("%d%d", &n, &m)) {
        v = vector < vector < int > >(n);
        ed = (1 << n) - 1;
        while (m--) {
            int x, y;
            scanf("%d %d", &x, &y);
            --x; --y;
            v[x].push_back(y);
            v[y].push_back(x);
        }
        printf("%d\n", dfs(0, 1));
    }
    return 0;
}