題目鏈接

暢通工程，可以用dijkstra算法實現。

聽說spfa很好用，來水一發

鄰接矩陣實現。

鄰接表待整理

#include <stdio.h>
#include <algorithm>
#include <cmath>
#include <cstring>
#include <deque>
#include <iomanip>
#include <iostream>
#include <list>
#include <map>
#include <queue>
#include 
 
<set>
#include <utility>
#include <vector>
#define mem(arr, num) memset(arr, 0, sizeof(arr))
#define _for(i, a, b) for (int i = a; i <= b; i++)
#define __for(i, a, b) for (int i = a; i >= b; i--)
#define IO                     \
  ios::sync_with_stdio(false);   cin.tie(0);                    cout.tie(
 
0);
using namespace std;
typedef long long ll;
const ll inf = 0x3f3f3f3f;
const double EPS = 1e-10;
const ll mod = 1000000007LL;
const int N = 200 + 5;
int mp[N][N], mp1[N][N];
int dis[N], vis[N];
int V, E;
void spfa(int start) {
  for (int i = 0; i <= V; i++) dis[i] = inf;
  dis[start] = 0;
  vis[start] = 1;
  queue
 
<int> q;
  q.push(start);
  while (!q.empty()) {
    int v = q.front();
    q.pop();
    vis[v] = 0;
    for (int i = 1; i <= mp1[v][0]; i++) {
      if (dis[mp1[v][i]] > dis[v] + mp[v][mp1[v][i]]) {
        dis[mp1[v][i]] = dis[v] + mp[v][mp1[v][i]];
        if (vis[mp1[v][i]] == 0) q.push(mp1[v][i]), vis[mp1[v][i]] = 1;
      }
    }
  }
}
int main() {
  int s, e, value;
  while (cin >> V >> E) {
    mem(mp,0); mem(mp1,0); mem(vis,0);
    _for(i, 1, E) {
      cin >> s >> e >> value;
      if (mp[s][e] != 0 && mp[s][e] < value) continue;
      mp1[s][0]++;
      mp1[s][mp1[s][0]] = e;
      mp[s][e] = value;  //記錄mp度並且記錄每個度的點的下標。
      mp1[e][0]++;
      mp1[e][mp1[e][0]] = s;
      mp[e][s] = value;
    }
    int start, _end;
    cin >> start >> _end;
    spfa(start);
    if (dis[_end] < inf)
      cout << dis[_end] << endl;
    else
      cout << "-1" << endl;
  }
  return 0;
}

hdu 1874 暢通工程（spfa 鄰接矩陣）