cf-Round #214 (Div. 2)-D-Dima and Trap Graph-dfs+二分

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<iostream>
using namespace std;
#define INF 99999999
#define maxn 4001
struct list
{
    int u;
    int v;
    int next;
    int l;
    int r;
}node[maxn*4];
int head[maxn];
int vis[maxn];
int nums;
int n,m;
void init()
{
    memset(head,-1,sizeof(head));
    memset(vis,0,sizeof(vis));
    nums=0;
}
void add(int a,int b,int l,int r)
{
    node[nums].u=a;
    node[nums].v=b;
    node[nums].l=l;
    node[nums].r=r;
    node[nums].next=head[a];
    head[a]=nums++;
}
int dfs(int st,int l,int r)
{
    if(l>r)return 0;
    vis[st]=1;
    if(st==n)return 1;
    for(int i=head[st];i!=-1;i=node[i].next)
    {
        if(vis[node[i].v])continue;
        if(node[i].l<=l&&node[i].r>=r)
        {
            if(dfs(node[i].v,l,r))return 1;
        }
    }
    return 0;
}
int main()
{
    int i,a,b,l,r;
    int fl[maxn];
    int fr[maxn];
    while(~scanf("%d%d",&n,&m))
    {
        init();
        for(i=1;i<=m;i++)
        {
            scanf("%d%d%d%d",&a,&b,&l,&r);
            add(a,b,l,r);
            add(b,a,l,r);
            fl[i]=l;
            fr[i]=r;
        }
        int ans=-1;
        sort(fl,fl+m+1);
        sort(fr,fr+m+1);
        for(i=1;i<=m;i++)
        {
            int l=1;
            int r=m+1;
            int mid=(l+r)/2;
            while(l<r)
            {
                memset(vis,0,sizeof(vis));
                if(dfs(1,fl[i],fr[mid]))l=mid+1;
                else r=mid;
                mid=(l+r)/2;
            }
            mid=mid-1;
            if(fl[i]<=fr[mid])
            {
                ans=max(ans,fr[mid]-fl[i]+1);
            }
        }
        if(ans==-1)
        {
            printf("Nice work, Dima!\n");
            continue;
        }
        printf("%d\n",ans);
    }
    return 0;
}