计蒜客 Skiing

题意：

        求最长路，记忆化搜索。

In this winter holiday, Bob has a plan for skiing at the mountain resort.

This ski resort has $M$ different ski paths and $N$ different flags situated at those turning points.

The $i$-th path from the SiS​i​​-th flag to the TiT​i​​-th flag has length LiL​i​​.

Each path must follow the principal of reduction of heights and the start point must be higher than the end point strictly.

An available ski trail would start from a flag, passing through several flags along the paths, and end at another flag.

Now, you should help Bob find the longest available ski trail in the ski resort.

Input Format

The first line contains an integer $T$, indicating that there are $T$ cases.

In each test case, the first line contains two integers $N$ and $M$ where $0<N\le 10000$ and $0<M\le 100000$ as described above.

Each of the following $M$ lines contains three integers SiS​i​​, TiT​i​​, and Li (0<Li<1000)L​i​​ (0<L​i​​<1000) describing a path in the ski resort.

Output Format

For each test case, ouput one integer representing the length of the longest ski trail.

样例输入

15 41 3 32 3 43 4 13 5 2

样例输出

6

题目来源

2017 ACM-ICPC 亚洲区（乌鲁木齐赛区）网络赛

#include<iostream>#include<vector>#include<algorithm>#include<cstdio>#include<cstring>#include<queue>using namespace std;struct node{    int next,dist;    node(int a,int b){next=a,dist=b;}};int num[10005];vector<node>G[10005];int dfs(int x){    if(num[x]) return num[x];    for(int i=0;i<G[x].size();i++)    {        int nx=G[x][i].next,dis=G[x][i].dist;        num[x]=max(num[x],dis+dfs(nx));    }    return num[x];}int main(){    int t;    int n,m;    int a,b,c;    scanf("%d",&t);    while(t--)    {        memset(num,0,sizeof(num));        scanf("%d%d",&n,&m);        for(int i=0;i<=n;i++)            G[i].clear();        while(m--)        {            scanf("%d%d%d",&a,&b,&c);            G[a].push_back(node(b,c));        }        int ans=0;        for(int i=1;i<=n;i++)            ans=max(ans,dfs(i));        printf("%d\n",ans);    }    return 0;}