POJ_2258 The settlers of Catan (DFS)

　　/*这题应该属于水题吧，基本不用什么大的处理，看懂题意就行。直接n次dfs，找出最大的length*/

//My Code: 16MS

#include <iostream>
#include <cstdio>
#include <cstring>

using namespace std;

const int N = 30;

int map[N][N];
bool vis[N][N];
int n;
int ans;

void dfs(int now, int t){
    int f, i;
    for(f = 1, i = 0; i < n; i++){
        if(vis[now][i] == false && map[now][i]){
            f = 0;
        }
    }
    //cout << f << endl;
    if(f) {ans = ans > t ? ans : t; return;}
    for(i = 0; i < n; i++){
        if(map[now][i] && !vis[now][i]){
            vis[now][i] = vis[i][now] = true;
            dfs(i, t+1);
            vis[now][i] = vis[i][now] = false;
        }
    }
}

int main(){
    //freopen("data.in", "r", stdin);

    int m, max, x, y, i;
    while(~scanf("%d%d", &n, &m)){
        if(n == 0 && m == 0)    break;
        memset(map, 0, sizeof(map));
        while(m--){
            scanf("%d%d", &x, &y);
            map[x][y] = map[y][x] = 1;
        }
        for(max = -1, i = 0; i < n; i++){
            memset(vis, false, sizeof(vis));
            ans = 0; dfs(i, 0);
            if(max < ans)
                max = ans;
        }
        printf("%d\n", max);
    }
}