Nyoj 42 stroke

One stroke problem time limit: 3000 MS | memory limit: 65535 kb difficulty: 4

Description

ZYC prefers to play games from an early age, including drawing a stroke. He wants to ask you to write a program for him to determine whether a graph can be used.

It is specified that all edges can be painted only once and cannot be repeated.

 

 

Input

The first row only has a positive integer n (n <= 10) indicating the number of test data groups.
The first row of each group of test data has two positive integers p, q (P <= 1000, q <= 2000), indicating the number of vertices and connections in the painting respectively. (The vertex number ranges from 1 to P)
In the next Q row, each row has two positive integers A and B (0 <a, B <p), indicating that there is a line between the two points numbered A and B.

Output

If there is a line that meets the conditions, the output is "yes ",
If no matching line exists, output "no ".

Sample Input

24 31 21 31 44 51 22 31 31 43 4

Sample output

Noyes

The following conditions must be met: 1. The graph is connected.
2. The odd degree node of the graph is 0 or 2.

DFS traversal is used here. Because a two-dimensional array is used to record graphs, it may cause a lot of unnecessary access and judgment. The efficiency is not very high, but it is still a. We recommend that you use the adjacent Table Record graph.

 1 #include<stdio.h> 2 bool visited[1005] = {false}; 3 int  dotin[1005] = {0}; 4 int graph[1005][1005]; 5 void dfs(int k, int n) 6 { 7     visited[k] = true; 8     int i,j; 9     for (i=k; i <= n; i++)10     {11         for (j=1; j <= n; j++)12             if (graph[k][j] != 0){13                 if (!visited[j])14                     dfs(j,n);15             }16     }17 }18 int main()19 {20     int n,p,q,a,b,i,j,dotnum = 0;21     bool yes = true;22     scanf("%d",&n);23     for (i=1; i < 1001; i++)24         for (j=1; j < 1001; j++)25             graph[i][j] = 0;26     while (n--)27     {28         scanf("%d%d",&p,&q);29         for (i=0; i < q; i++)30         {31             scanf("%d%d",&a,&b);32             graph[a][b] = 1;33             graph[b][a] = 1;34             dotin[a]++;35             dotin[b]++;36         }37     dfs(1,p);38     for (i=1; i <= p; i++)39         if (!visited[i])40         {41             yes = false;42             break;43         }44     for (i=1; i <= p; i++)45         if (dotin[i]%2)46             dotnum++;47     if ((yes && dotnum == 2) || (yes && dotnum == 0))48         printf("Yes\n");49     else50         printf("No\n");51     yes = true;52     dotnum = 0;53     for (i=1; i <= p; i++)54         dotin[i] = 0;55     for (i=1; i <= p; i++)56         visited[i] = false;57     for (i=1; i <= p; i++)58         for (j=1; j <= p; j++)59             graph[i][j] = 0;60     }61 }

 

Nyoj 42 stroke