欧拉回路 (Euler Circuit) POJ 1780

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

#define MAXN    100000
#define MAXM    1000000

struct edge {
int id;
int to;
int next;
};

int adjlist[MAXN]; int nnodes;
edge edges[MAXM]; int nedges;

int stack[MAXM]; int top;
int visited[MAXM];
int result[MAXM + 10]; int nres;

int n; // input

void graph_init() {
nnodes = 1;
int k = n - 1;
while (k--) nnodes *= 10;
int size = nnodes * sizeof(int);
memset(adjlist, -1, size);
nedges = 0;
top = -1;
memset(visited, 0, size * 10);
nres = 0;
}

void add_edge(int u, int v, int eid) {
edges[nedges].id = eid;
edges[nedges].to = v;
edges[nedges].next = adjlist[u];
adjlist[u] = nedges++;
}

void graph_dfs() {
stack[++top] = 0;
printf("%0*d", n-1, 0);
visited[0] = 1;
while (top >= 0) {
int u = stack[top];
for (int i = adjlist[u]; i != -1; i = edges[i].next) {
int eid = edges[i].id;
int v = edges[i].to;
if (visited[eid] == 0) {
visited[eid] = 1;
stack[++top] = v;
goto cont_while;
}
}
top--;
result[nres++] = u;
cont_while: ;
}
for (int i = nres - 1; i >= 0; i--)
printf("%d", result[i] % 10);
printf("\n");
}

void solve() {
graph_init();
for (int u = 0; u < nnodes; u++) {
int w = u % (nnodes / 10);
for (int j = 9; j >= 0; j--) {
int v = w * 10 + j;
add_edge(u, v, u*10+j);
}
}
graph_dfs();
}

int main() {
while (scanf("%d", &n) != EOF) {
if (n == 0) break;
if (n == 1) printf("0123456789\n");
else solve();
}
return 0;
}