P1250 种树

Posted 2020-12-02 garen-wang

队列有毒。。。

---

当然是差分约束了！

两个条件：(a_r - a_{l - 1} geq c) 和 (0 geq a_i - a_{i - 1} leq 1)

这里统一化为大于等于，成为最长路。

直接求出最长路即可。

PS：队列抽风了。。。有STL的队列才过了。我是不是得退役了。。。

代码：

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<queue>
const int maxn = 30005, maxm = 50005;
struct Edges
{
    int next, to, weight;
} e[maxm << 4];
int head[maxn], tot;
int n, m;
bool vis[maxn];
int dist[maxn];
std::queue<int> q;
void link(int u, int v, int w)
{
    e[++tot] = (Edges){head[u], v, w};
    head[u] = tot;
}
void spfa(int s)
{
    memset(dist, -1, sizeof(dist));
    dist[s] = 0;
    q.push(s); vis[s] = true;
    while(!q.empty())
    {
        int u = q.front(); q.pop(); vis[u] = false;
        for(int i = head[u]; i != -1; i = e[i].next)
        {
            int v = e[i].to;
            if(dist[u] + e[i].weight > dist[v])
            {
                dist[v] = dist[u] + e[i].weight;
                if(!vis[v])
                {
                    q.push(v); vis[v] = true;
                }
            }
        }
    }
}
int main()
{
    memset(head, -1, sizeof(head));
    scanf("%d%d", &n, &m);
    while(m--)
    {
        int l, r, c; scanf("%d%d%d", &l, &r, &c);
        //a[r] - a[l - 1] >= c
        link(l - 1, r, c);
    }
    for(int i = 1; i <= n; i++)
    {
        //0 <= a[i] - a[i - 1] <= 1
        //a[i] - a[i - 1] >= 0
        //a[i - 1] - a[i] >= -1
        link(i - 1, i, 0);
        link(i, i - 1, -1);
    }
    spfa(0);
    printf("%d
", dist[n]);
    return 0;
}