codeforces 232A Cycles (构建图，贪心+模拟）

                                                  Cycles

Description
描述
John Doe started thinking about graphs. After some thought he decided that he wants to paint an undirected graph, containing exactly kcycles of length 3.
A cycle of length 3 is an unordered group of three distinct graph vertices a, b and c, such that each pair of them is connected by a graph edge.
John has been painting for long, but he has not been a success. Help him find such graph. Note that the number of vertices there shouldn't exceed 100, or else John will have problems painting it.
Input
输入
A single line contains an integer k (1 ≤ k ≤ 105) — the number of cycles of length 3 in the required graph.
Output
输出
In the first line print integer n (3 ≤ n ≤ 100) — the number of vertices in the found graph. In each of next n lines print n characters "0" and "1": the i-th character of the j-th line should equal "0", if vertices i and j do not
have an edge between them, otherwise it should equal "1". Note that as the required graph is undirected, the i-th character of the j-th line must equal the j-th character of the i-th line. The graph shouldn't contain self-loops, so the i-th character of the
i-th line must equal "0" for all i.

Sample Input

Input

1

Output

3
011101110

Input

10

Output

5
0111110111110111110111110

贪心手法。点最多一百个，那么，要让每个点的作用都发挥出来。所有，可以模拟每次加入点所带来的影响，来确定，两个点是否要连接。

#include <iostream>
#include<cstdio>
using namespace std;
int ans,k,ss;
int gra[103][103];
int main()
{
int n,i,j,k;
scanf("%d",&n);
gra[1][2]=gra[2][1]=1;//最少存在一条边
for(i=3;i<=100;i++)//依次增加顶点
{
for(j=1;j<i;j++)
{
ss=0;//三元环个数
for(k=1;k<j;k++)
if(gra[k][j]&&gra[k][i])
ss++;
if(n>=ss)
{
n-=ss;
gra[i][j]=gra[j][i]=1;
}
if(n==0)break;
}
if(n==0)break;
}
n=i;
printf("%d\n",n);
for(i=1;i<=n;i++)
{
for(j=1;j<=n;j++)
printf("%d",gra[i][j]);
printf("\n");
}
return 0;
}