HDU 3249 Test for job （有向無環圖上的最長路，DP）
阿新 • • 發佈：2017-06-04
code head struct sin == cout article scanf for
??
解題思路：
求有向無環圖上的最長路。簡單的動態規劃
#include <iostream>
#include <cstring>
#include <cstdlib>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cmath>
#define LL long long
using namespace std;
const int MAXN = 100000 + 10;
const int MAXM = 1000000 + 10;
const LL INF = -1 * 20000 * 100000 - 10;
struct Edge
{
int to, next;
}edge[MAXM];
int tot, head[MAXN];
LL w[MAXN];
LL dp[MAXN];
int out[MAXN], vis[MAXN];
int n, m;
void init()
{
tot = 0;
memset(head, -1, sizeof(head));
memset(w, 0, sizeof(w));
memset(dp, INF, sizeof(dp));
memset(vis, 0, sizeof(vis));
memset(out, 0, sizeof(out));
}
void addedge(int u, int v)
{
edge[tot].to = v;
edge[tot].next = head[u];
head[u] = tot++;
}
int dfs(int u)
{
//cout << u << endl;
if(vis[u]) return dp[u];
vis[u] = 1;
for(int i=head[u];i!=-1;i=edge[i].next)
{
int v = edge[i].to;
dp[u] = max(dp[u], (LL)dfs(v));
}
if(head[u] == -1) return dp[u] = w[u];
else return dp[u] = (dp[u] + w[u]);
// return dp[u];
}
int main()
{
while(scanf("%d%d", &n, &m)!=EOF)
{
init();
for(int i=1;i<=n;i++) scanf("%d", &w[i]);
int u, v;
for(int i=1;i<=m;i++)
{
scanf("%d%d", &u, &v);
addedge(v, u);
out[u]++;
}
LL ans = INF;
//for(int i=1;i<=n;i++) cout << dp[i] << ‘ ‘;
for(int i=1;i<=n;i++) if(!out[i])ans = max(ans, (LL)dfs(i));
printf("%d\n", ans);
}
return 0;
}
HDU 3249 Test for job （有向無環圖上的最長路，DP）