Time Limit: 2000/1000MS (Java/Others)
Memory Limit: 128000/64000KB (Java/Others)
Submit Statistic Next Problem
Problem Description
Let us consider undirected graph G = {V; E} which has N vertices and M edges. Incidence matrix of this graph is N × M matrix A = {a
i,j}, such that a
i,j is 1 if i-th vertex is one of the ends of j -th edge and 0 in the other case. Your task is to find the sum of all elements of the matrix A
TA.
Input
The first line of the input file contains two integer numbers — N and M (2 ≤ N ≤ 10 000, 1 ≤ M ≤100 000). Then 2*M integer numbers follow, forming M pairs, each pair describes one edge of the graph. All edges are different and there are no loops (i.e. edge ends are distinct).
Output
Output the only number — the sum requested.
Sample Input
Sample Output
18
其实就是一个矩阵,自己乘自己,画图可以秒懂
java:
import java.util.*;
import java.io.*;
import java.math.*;
public class Main{
static final int MAXN = 10000 + 5;
static int [] mp = new int[MAXN];
public static void main(String [] agrv)
throws IOException
{
//System.setIn(new FileInputStream(new File("D:" + File.separator + "imput.txt")));
Scanner cin = new Scanner(System.in);
int N, M, u, v;
while(cin.hasNext()){
N = cin.nextInt();
M = cin.nextInt();
Arrays.fill(mp, 1, N + 1, 0);
for(int i = 1;i <= M ;i ++){
u = cin.nextInt();
v = cin.nextInt();
if(u == v) mp[v] ++;
else {
mp[v] ++;
mp[u] ++;
}
}
long ans = 0;
for(int i = 1;i <= N;i ++){
ans += (long)mp[i] * mp[i];
}
System.out.println(ans);
}
}
}