POJ-2258

#include <stdio.h>
#include <string.h>
int node[25][25];
int rear[25], visit[25];
int edges[25][25];
int max;

void dfs(int n, int lenght)
{
     int i;
     
     if (lenght > max)
        max = lenght;
     for (i = 0; i < rear[n]; i++) {
         if (!edges[n][node[n][i]] && !edges[node[n][i]][n]) {
            edges[n][node[n][i]] = 1;
            edges[node[n][i]][n] = 1;
            dfs(node[n][i], lenght+1);
            edges[n][node[n][i]] = 0;
            edges[node[n][i]][n] = 0;
         }
     }
}

int main()
{
    int n, m;
    int i;
    int a, b;
    while (scanf("%d%d", &n, &m), n||m) {
          memset(rear, 0, sizeof(rear));
          max = 0;
          for (i = 0; i < m; i++) {
              scanf("%d%d", &a, &b);             
              node[a][rear[a]++] = b;
              node[b][rear[b]++] = a;
          }
          for (i = 0; i < n; i++) {           
              dfs(i, 0);
          }
          printf("%d\n", max);
    }
    return 0;
}