2017 ACM-ICPC 亚洲区(乌鲁木齐赛区) 网络赛 H.Skiing(求有向无环图的最长路)

#include <iostream>
#include <cstdio>
#include <fstream>
#include <algorithm>
#include <cmath>
#include <deque>
#include <vector>
#include <queue>
#include <string>
#include <cstring>
#include <map>
#include <stack>
#include <set>
#define Max(a,b) a>b?a:b
#define Min(a,b) a>b?b:a
#define mem(a,b) memset(a,b,sizeof(a))
using namespace std;
typedef long long ll;
int dir[4][2]= {{1,0},{-1,0},{0,1},{0,-1}};
const double eps = 1e-6;
const double Pi = acos(-1.0);
const int INF=0x3f3f3f3f;

int vel[100005];
ll dis[100005], ans;
int in[100005];//记录每个点的入度
int out[100005];//记录每个点的出度
int head[100005], len;//head[i]=j表示以i为起点的边的编号为j
int n, m;
int tnum[100005], nnum[100005];

struct edge
{
int to,val,next;
}e[1000005];

void add(int from,int to,int val)
{
e[len].to=to;
e[len].val=val;
e[len].next=head[from];
head[from]=len++;
}
void TopSort()
{
priority_queue<int, vector<int>, greater<int> > q;//优先队列 按照由小到大的顺序

q.push(0);
int cnt = 0;
while(!q.empty())
{
int u = q.top();
q.pop();
cnt++;
tnum[u] = cnt;//从1开始记录出队的顺序
for(int i=head[u]; i!=-1; i=e[i].next)
{
int v = e[i].to;
in[v]--;
if(!in[v])
q.push(v);
}
}

dis[0] = 0;
for(int i=1; i<=n; i++)
nnum[tnum[i]-1] = i;  //比如tnum[u] = 1表示点u是第1个出队的，那么nnum[tnum[u] - 1] = u -> nnum[0] = u,
//这样nnum[i] = j就维护了第i个出队的点是j

for(int i=0; i<=n; i++)
{
for(int j=head[nnum[i]]; j!=-1; j=e[j].next)
{
int t = e[j].to;
dis[t] = max(dis[t], dis[nnum[i]]+e[j].val);
}
}
}
int main()
{
int t;
scanf("%d", &t);
while(t--)
{
scanf("%d%d", &n, &m);

len = 0;
ans = -INF;
fill(dis, dis+n+1,-INF);
mem(in, 0);
mem(out, 0);
mem(head, -1);

for(int i=1; i<=m; i++)
{
int x, y, v;
scanf("%d%d%d", &x, &y, &v);
add(x, y, v);
out[x]++;
in[y]++;
}
for(int i=1; i<=n; i++)
if(!in[i])
{
add(0, i, 0);
out[0]++;
in[i]++;
}
TopSort();

//
for(int i=1; i<=n; i++)
if(out[i]==0)
ans = max(ans, dis[i]);

printf("%lld\n", ans);
}
}