B. Fox and Minimal path
题目连接:
http://codeforces.com/contest/388/problem/B
Description
Fox Ciel wants to write a task for a programming contest. The task is: “You are given a simple undirected graph with n vertexes. Each its edge has unit length. You should calculate the number of shortest paths between vertex 1 and vertex 2.”
Same with some writers, she wants to make an example with some certain output: for example, her birthday or the number of her boyfriend. Can you help her to make a test case with answer equal exactly to k?
Input
The first line contains a single integer k (1 ≤ k ≤ 109).
Output
You should output a graph G with n vertexes (2 ≤ n ≤ 1000). There must be exactly k shortest paths between vertex 1 and vertex 2 of the graph.
The first line must contain an integer n. Then adjacency matrix G with n rows and n columns must follow. Each element of the matrix must be ‘N’ or ‘Y’. If Gij is ‘Y’, then graph G has a edge connecting vertex i and vertex j. Consider the graph vertexes are numbered from 1 to n.
The graph must be undirected and simple: Gii = ‘N’ and Gij = Gji must hold. And there must be at least one path between vertex 1 and vertex 2. It’s guaranteed that the answer exists. If there multiple correct answers, you can output any of them.
Sample Input
2
Sample Output
4
NNYY
NNYY
YYNN
YYNN
Hint
题意
你需要构造一个图,使得1到2的最短路恰好有k条
题解:
拆成二进制,比如9 = 2^0+2^3
二进制的最短路就非常好构造,就2*2*2这样去构造就好了
然而这样裸的构造的话,点数可能会超过1000个点
所以你再压缩一下点的个数,复用一下就好了
代码
#include<bits/stdc++.h>
using namespace std;
const int maxn = 3200;
int mp[maxn][maxn];
int k,bit[32],tot=3,max_len;
int getid()
{
return tot++;
}
int main()
{
scanf("%d",&k);
int id1=1,id2=1,id3=getid();
while(k)
{
if(k%2)mp[id1][id3]=1,mp[id2][id3]=1;
k/=2;if(k==0)break;
int id4=getid(),id5=getid(),id6=getid();
mp[id1][id4]=1,mp[id1][id5]=1;
mp[id2][id4]=1,mp[id2][id5]=1;
mp[id3][id6]=1;
id1=id4,id2=id5,id3=id6;
}
mp[id3][2]=1;
int Max = getid()-1;
printf("%d\n",Max);
for(int i=1;i<=Max;i++,cout<<endl)for(int j=1;j<=Max;j++)
if(mp[i][j]||mp[j][i])printf("Y");else printf("N");
}