割点-危险系数

朱雀 2022-07-12 12:15 195阅读 0赞

package 搜索.割点;  
  
  
import java.io.BufferedInputStream;  
import java.io.IOException;  
import java.util.Arrays;  
  
  
public class 危险系数 \{  
static BufferedInputStream bs = new BufferedInputStream(System.in);  
  
  
static int readInt() throws IOException \{  
int num = 0;  
int i = 0;  
boolean flag = false;  
while (((i = bs.read()) & 48) != 48 || i > 57) \{  
if (i == 45)  
flag = true;  
\}  
while ((i & 56) == 48 || (i & 62) == 56) \{  
num = num \* 10 + (i & 15);  
i = bs.read();  
\}  
if (flag)  
num = -num;  
return num;  
\}  
  
  
static class Edge \{  
public int to;  
public int next;  
\}  
  
  
static int head\[\];  
static Edge\[\] edge;  
static int top;  
static boolean flag\[\];  
static int n;  
static int m;  
static int cnt\[\];  
static int way\[\];  
static int sum;  
  
  
public static void main(String\[\] args) throws IOException \{  
n = readInt();  
m = readInt();  
cnt = new int\[n + 1\];  
way = new int\[n + 1\];  
flag = new boolean\[n + 1\];  
edge = new Edge\[m \* 2\];  
head = new int\[m \* 2\];  
Arrays.fill(head, -1);  
for (int i = 0; i < m; i++) \{  
int u = readInt();  
int v = readInt();  
addEdge(u, v);  
addEdge(v, u);  
\}  
  
  
dfs(readInt(), readInt(), 0);  
operation();  
  
  
\}  
  
  
private static void operation() \{  
int result = 0;  
for (int i = 1; i <= n; i++) \{  
if (cnt\[i\] == sum)  
result++;  
\}  
System.out.println(result - 2);  
\}  
  
  
private static void dfs(int u, int v, int count) \{  
flag\[u\] = true;  
way\[count\] = u;  
if (u == v) \{  
sum++;  
for (int i = 0; i <= count; i++) \{  
cnt\[way\[i\]\]++;  
\}  
\} else \{  
for (int i = head\[u\]; i != -1; i = edge\[i\].next) \{  
int to = edge\[i\].to;  
if (!flag\[to\]) \{  
dfs(to, v, count + 1);  
// flag\[u\] = false;  
\}  
\}  
\}  
flag\[u\] = false;  
\}  
  
  
private static void addEdge(int u, int v) \{  
edge\[top\] = new Edge();  
edge\[top\].to = v;  
edge\[top\].next = head\[u\];  
head\[u\] = top++;  
  
  
\}  
\}