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  • computer（hdu2196）

    Computer

    Time Limit: 1000/1000 MS (Java/Others)    Memory Limit: 32768/32768 K (Java/Others)
    Total Submission(s): 6378    Accepted Submission(s): 3211


    Problem Description
    A school bought the first computer some time ago(so this computer's id is 1). During the recent years the school bought N-1 new computers. Each new computer was connected to one of settled earlier. Managers of school are anxious about slow functioning of the net and want to know the maximum distance Si for which i-th computer needs to send signal (i.e. length of cable to the most distant computer). You need to provide this information. 


    Hint: the example input is corresponding to this graph. And from the graph, you can see that the computer 4 is farthest one from 1, so S1 = 3. Computer 4 and 5 are the farthest ones from 2, so S2 = 2. Computer 5 is the farthest one from 3, so S3 = 3. we also get S4 = 4, S5 = 4.
     
    Input
    Input file contains multiple test cases.In each case there is natural number N (N<=10000) in the first line, followed by (N-1) lines with descriptions of computers. i-th line contains two natural numbers - number of computer, to which i-th computer is connected and length of cable used for connection. Total length of cable does not exceed 10^9. Numbers in lines of input are separated by a space.
     
    Output
    For each case output N lines. i-th line must contain number Si for i-th computer (1<=i<=N).
     
    Sample Input
    5
    1 1
    2 1
    3 1
    1 1
     
    Sample Output
    3
    2
    3
    4
    4
     
     
    Author
    scnu
     
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    lcy   |   We have carefully selected several similar problems for you:  1011 3456 1520 2242 1059 
    题意：给n个点，1为根节点，给你的是棵树，然后找到各个节点离树上其他节点最远的距离;
    思路：树形dp；
    因为这是一颗树，除了根节点外其他每个节点都又且一个父亲节点，首先dfs更新每个节点到其子节点下端的最长距离和次长距离，然后最长距离还可能从父亲节点那更新。那么再dfs从父亲节点更新子节点的最长距离，这个时候，父亲节点的最长可能是通过当前要更新的子节点，那么就用次长路去更新。复杂度O（n）；
      1 #include<iostream>
  2 #include<string.h>
  3 #include<algorithm>
  4 #include<queue>
  5 #include<math.h>
  6 #include<stdlib.h>
  7 #include<stack>
  8 #include<stdio.h>
  9 #include<ctype.h>
 10 #include<map>
 11 #include<vector>
 12 #include<map>
 13 using namespace std;
 14 typedef struct acc
 15 {
 16     int id;
 17     int val;
 18 } ak;
 19 vector<ak>vec[100005];
 20 bool vis[100005];
 21 typedef struct node
 22 {
 23     int id;
 24     int mcost;
 25     int scost;
 26     int mid;
 27     int sid;
 28     node()
 29     {
 30         mcost = 0;
 31         scost = 0;
 32         mid = -1;
 33         sid = -1;
 34     }
 35 } ss;
 36 ss dp[100005];
 37 int father[1000005];
 38 void dfs1(int n);
 39 void dfs2(int n);
 40 int main(void)
 41 {
 42     int n,m;
 43     while(scanf("%d",&n)!=EOF)
 44     {
 45         memset(father,-1,sizeof(father));
 46         int i,j;
 47         memset(dp,0,sizeof(dp));
 48         for(i = 0; i < 100005; i++)
 49             vec[i].clear();
 50         for(i = 2; i <= n; i++)
 51         {
 52             int id,val;
 53             scanf("%d %d",&id,&val);
 54             ak a;
 55             a.val = val;
 56             a.id = i;
 57             father[i] = id;
 58             vec[id].push_back(a);
 59         }
 60         dfs1(1);
 61         dfs2(1);
 62         for(i = 1; i <= n; i++)
 63         {
 64             printf("%d
",dp[i].mcost);
 65         }
 66     }
 67     return 0;
 68 }
 69 void dfs1(int n)
 70 {
 71     for(int i = 0; i < vec[n].size(); i++)
 72     {
 73         ak d = vec[n][i];
 74         {
 75             dfs1(d.id);
 76             if(dp[d.id].mcost+d.val > dp[n].mcost)
 77             {
 78                 dp[n].scost = dp[n].mcost;
 79                 dp[n].sid = dp[n].mid;
 80                 dp[n].mcost = dp[d.id].mcost+d.val;
 81                 dp[n].mid = d.id;
 82             }
 83             else if(dp[d.id].mcost+d.val > dp[n].scost)
 84             {
 85                 dp[n].scost = dp[d.id].mcost+d.val;
 86                 dp[n].sid = d.id;
 87             }
 88         }
 89     }
 90 }
 91 void dfs2(int n)
 92 {
 93     for(int i = 0; i < vec[n].size(); i++)
 94     {
 95         ak d = vec[n][i];
 96         if(dp[n].mid!=d.id)
 97         {
 98             if(dp[n].mcost + d.val > dp[d.id].mcost)
 99             {
100                 dp[d.id].scost = dp[d.id].mcost;
101                 dp[d.id].sid = dp[d.id].mid;
102                 dp[d.id].mcost = dp[n].mcost + d.val;
103                 dp[d.id].mid = n;
104             }
105             else if(dp[n].mcost + d.val > dp[d.id].scost)
106             {
107                 dp[d.id].scost = dp[n].mcost + d.val;
108                 dp[d.id].sid = n;
109             }
110         }
111         else
112         {
113               if(dp[n].scost + d.val > dp[d.id].mcost)
114             {
115                 dp[d.id].scost = dp[d.id].mcost;
116                 dp[d.id].sid = dp[d.id].mid;
117                 dp[d.id].mcost = dp[n].scost + d.val;
118                 dp[d.id].mid = n;
119             }
120             else if(dp[n].scost + d.val > dp[d.id].scost)
121             {
122                 dp[d.id].scost = dp[n].scost + d.val;
123                 dp[d.id].sid = n;
124             }
125         }
126         dfs2(d.id);
127     }
128 }
     
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  • 原文地址：https://www.cnblogs.com/zzuli2sjy/p/6232574.html
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