洛谷 P1137 旅行计划

旅行计划

待证明这样dp的正确性。

#include <iostream>
#include <cstdio>
#include <cstring>
#include <queue>
using namespace std;
//Mystery_Sky
//
#define maxn 1000010
#define maxm 5000050
#define INF 0x3f3f3f3f;
queue <int> q;
int head[maxn], ind[maxn], cnt, dis[maxn];
int n, m;
struct Edge{
    int to, next;
}edge[maxn];

inline void add_edge(int u, int v)
{
    edge[++cnt].to = v;
    edge[cnt].next = head[u];
    head[u] = cnt;
}

inline void topo()
{
    for(int i = 1; i <= n; i++) {
        if(!ind[i]) {
            q.push(i);
            dis[i]++; 
        }
    }
    while(!q.empty()) {
        int u = q.front();
        q.pop();
        for(int i = head[u]; i; i = edge[i].next) {
            int v = edge[i].to;
            dis[v] = max(dis[v], dis[u]+1);
            if(!--ind[v]) q.push(v); 
        }
    }
}

int main() {
    scanf("%d%d", &n, &m);
    int u, v;
    for(int i = 1; i <= m; i++) {
        scanf("%d%d", &u, &v);
        add_edge(u, v);
        ind[v]++;
    }
    topo();
    for(int i = 1; i <= n; i++) printf("%d\n", dis[i]);
    return 0;
}