[BZOJ1663] [Usaco2006 Open]赶集（spfa最长路）

传送门

按照时间t排序

如果 t[i] + map[i][j] <= t[j]，就在i和j之间连一条边

然后spfa找最长路

#include <queue>
#include <cstdio>
#include <cstring>
#include <iostream>
#include <algorithm>
#define N 401

using namespace std;

int n, ans, cnt;
int a

, map

, dis
, head
, to[N * 100], next[N * 100];
bool vis
;
queue <int> q;

struct node
{
int t, id;
}p
;

inline int read()
{
int x = 0, f = 1;
char ch = getchar();
for(; !isdigit(ch); ch = getchar()) if(ch == '-') f = -1;
for(; isdigit(ch); ch = getchar()) x = (x << 1) + (x << 3) + ch - '0';
return x * f;
}

inline bool cmp(node x, node y)
{
return x.t < y.t;
}

inline void spfa()
{
int i, u, v;
q.push(0);
while(!q.empty())
{
u = q.front();
q.pop();
vis[u] = 0;
for(i = head[u]; ~i; i = next[i])
{
v = to[i];
if(dis[v] < dis[u] + 1)
{
dis[v] = dis[u] + 1;
if(!vis[v])
{
q.push(v);
vis[v] = 1;
}
}
}
}
}

inline void add(int x, int y)
{
to[cnt] = y;
next[cnt] = head[x];
head[x] = cnt++;
}

int main()
{
int i, j, k;
n = read();
memset(head, -1, sizeof(head));
for(i = 1; i <= n; i++)
p[i].id = i, p[i].t = read();
for(i = 1; i <= n; i++)
for(j = 1; j <= n; j++)
map[i][j] = read();
sort(p + 1, p + n + 1, cmp);
for(i = 1; i <= n; i++) map[0][i] = map[1][i];
p[0].id = p[0].t = 0;
for(i = 0; i <= n; i++)
for(j = i + 1; j <= n; j++)
if(p[i].t + map[p[i].id][p[j].id] <= p[j].t)
add(p[i].id, p[j].id);
spfa();
for(i = 1; i <= n; i++) ans = max(ans, dis[i]);
printf("%d\n", ans);
return 0;
}