HDU6026 Deleting Edges
2017-05-07 19:30
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Deleting Edges
Time Limit: 2000/1000 MS (Java/Others) MemoryLimit: 131072/131072 K (Java/Others)
Total Submission(s): 18 Accepted Submission(s): 9
Problem Description
Little Q is crazy about graph theory, and now he creates a game about graphs and trees.
There is a bi-directional graph with n nodes,
labeled from 0 to n−1.
Every edge has its length, which is a positive integer ranged from 1 to 9.
Now, Little Q wants to delete some edges (or delete nothing) in the graph to get a new graph, which satisfies the following requirements:
(1) The new graph is a tree with n−1 edges.
(2) For every vertice v(0<v<n),
the distance between 0 and v on
the tree is equal to the length of shortest path from 0 to v in
the original graph.
Little Q wonders the number of ways to delete edges to get such a satisfied graph. If there exists an edge between two nodes i and j,
while in another graph there isn't such edge, then we regard the two graphs different.
Since the answer may be very large, please print the answer modulo 109+7.
Input
The input contains several test cases, no more than 10 test cases.
In each test case, the first line contains an integer n(1≤n≤50),
denoting the number of nodes in the graph.
In the following n lines,
every line contains a string with n characters.
These strings describes the adjacency matrix of the graph. Suppose the j-th
number of the i-th
line is c(0≤c≤9),
if c is
a positive integer, there is an edge between i and j with
length of c,
if c=0,
then there isn't any edge between i and j.
The input data ensure that the i-th
number of the i-th
line is always 0, and the j-th
number of the i-th
line is always equal to the i-th
number of the j-th
line.
Output
For each test case, print a single line containing a single integer, denoting the answer modulo 109+7.
Sample Input
2
01
10
4
0123
1012
2101
3210
Sample Output
1
6
Source
2017中国大学生程序设计竞赛 - 女生专场
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题目的意思是给出一张图,求最短路数的个数有多少种
思路:求出最短路,在求最短路时记录到达每个点的方案数,结果就是所有点方案数之和
#include <iostream> #include <cstdio> #include <cstring> #include <string> #include <algorithm> #include <cmath> #include <map> #include <cmath> #include <set> #include <stack> #include <queue> #include <vector> #include <bitset> #include <functional> using namespace std; #define LL long long const int INF=0x3f3f3f3f; const int mod=1e9+7; int n,m; int mp[55][55]; int dis[55]; int vis[55]; LL cnt[55]; struct node { int id,val; friend bool operator<(node a,node b) { return a.val>b.val; } }; void djstl(int o) { memset(dis,INF,sizeof dis); memset(vis,0,sizeof vis); memset(cnt,0,sizeof cnt); node f,d; f.id=o,f.val=0; priority_queue<node>q; q.push(f); vis[o]=cnt[o]=1,dis[o]=0; while(!q.empty()) { f=q.top(); q.pop(); vis[f.id]=1; for(int i=0; i<n; i++) { if(!vis[i]&&f.val+mp[f.id][i]<dis[i]) { dis[i]=f.val+mp[f.id][i]; cnt[i]=1; d.id=i; d.val=dis[i]; q.push(d); } else if(!vis[i]&&f.val+mp[f.id][i]==dis[i]) { cnt[i]++; } } } } int main() { char s[55]; while(~scanf("%d",&n)) { memset(mp,INF,sizeof mp); for(int i=0; i<n; i++) { scanf("%s",&s); for(int j=0; j<n; j++) if(s[j]!='0') mp[i][j]=s[j]-'0'; } djstl(0); LL ans=1; for(int i=0; i<n; i++) { ans*=cnt[i]; ans%=mod; } printf("%d\n",ans); } return 0; }
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