专题四 · 1010

Posted 2023-02-06 suamfadmp

代码及解释

#include <stdio.h>

#include <iostream>
#include <queue>

// 最短路之后深搜
// 用的队列优化
//
//

typedef struct n1  int distens, flog;  node;

node N[1005];
int map[1005][1005], k;
int direct[1005];


void set(int n) 
  int i, j, m, n1, n2, d;
  for (i = 1; i <= n; i++) 
    for (j = 1; j <= n; j++) 
      map[i][j] = -1;
    
    N[i].distens = 10000000;
    N[i].flog = 0;
    direct[i] = 0;
  

  scanf("%d", &m);
  while (m--) 
    scanf("%d%d%d", &n1, &n2, &d);
    if (map[n1][n2] != 0 || map[n1][n2] > d)
      map[n1][n2] = map[n2][n1] = d;
  

void spfa(int n) 
  std::queue<int> Q;
  int now;
  int i;

  N[2].distens = 0;
  N[2].flog = 1;

  Q.push(2);
  while (!Q.empty()) 

    now = Q.front();
    Q.pop();
    N[now].flog = 0;

    for (i = 1; i <= n; i++)
      if (map[now][i] != -1) 
        if (N[i].distens > N[now].distens + map[now][i]) 
          N[i].distens = N[now].distens + map[now][i];
          if (N[i].flog == 0) 
            N[i].flog = 1;
            Q.push(i);
          
        
      


  

int DFS(int now, int n) 
  int i;
  if (direct[now] > 0)
    return direct[now];

  if (now == 2) 
    return 1;
  

  for (i = 1; i <= n; i++)
    if (map[now][i] != -1 && N[now].distens > N[i].distens)
      direct[now] += DFS(i, n);

  return direct[now];


int main() 
  int n;
  while (scanf("%d", &n) > 0 && n) 
    set(n);
    spfa(n);
    k = DFS(1, n);
    printf("%d\\n", k);