HDU-2544-最短路(各种最短路径算法)

• 迪杰斯特拉算法--O(n^2)

  #include"iostream"
  #include"cstring"
  #include"cstdio"
  using namespace std;
  const int inf = 0x3f3f3f3f;
  typedef long long LL;
  int map[105][105];
  int ans[105], n, m;
  bool flag[105];
  void dij() {
      for(int i = 2; i <= n; i++)
      ans[i] = map[1][i];
      ans[1] = 0;
      memset(flag, true, sizeof(flag));
      flag[1] = false;
      for(int i = 2; i < n; i++) {
          int v, mn = inf;
          for(int j = 1; j <= n; j++)
          // 此处建议用 <= 因为map和mx都是初始化为inf，如果用 < 可能一个都找不到导致v是随机值而产生RE。当然也可采用其他方式避免v的随机值；
          if(ans[j] <= mn && flag[j]) {
              mn = ans[j];
              v = j;
          }
          for(int j = 1; j <= n; j++)
          if(ans[v] + map[v][j] < ans[j])
          ans[j] = ans[v] + map[v][j];
          flag[v] = false;
      }
  }
  int main() {
      int a, b, c;
      while(scanf("%d%d", &n, &m) && (n || m)) {
          memset(map, inf, sizeof(map));
          while(m--) {
              scanf("%d%d%d", &a, &b, &c);
              if(map[a][b] > c)
              map[a][b] = map[b][a] = c;
          }
          dij();
          printf("%d
  ", ans[n]);
      }
      return 0;
  }

• 迪杰斯特拉算法堆优化--O(nlgn) 以链式前向星建图

  #include "bits/stdc++.h"
  using namespace std;
  typedef pair<int, int> PII;
  const int MAXN = 10005;
  const int INF = 0x3f3f3f3f;
  struct Edge {
      int t, w, n;
  } edge[MAXN << 1];
  int tot, tail[MAXN], dis[MAXN];
  bool use[MAXN];
  void add(int u, int v, int w) {
      edge[tot].t = v;
      edge[tot].w = w;
      edge[tot].n = tail[u];
      tail[u] = tot++;
  }
  void dij() {
      memset(dis, INF, sizeof(dis));
      memset(use, false, sizeof(use));
      // PII的first表示权重，second表示节点。后面部分是为了让优先队列每次取最小值 
      priority_queue<PII, vector<PII>, greater<PII> > que;
      for (int i = tail[1]; i != -1; i = edge[i].n) {
          int t = edge[i].t;
          int w = edge[i].w;
          if (w < dis[t]) {
              dis[t] = w;
              que.push({w, t});
          } 
      }
      use[1] = true;
      while (!que.empty()) {
          int v = que.top().second;
          que.pop();
          if (use[v]) continue;
          use[v] = true;
          for (int i = tail[v]; i != -1; i = edge[i].n) {
              int t = edge[i].t;
              int w = edge[i].w;
              if (dis[v] + w < dis[t]) {
                  dis[t] = dis[v] + w;
                  que.push({dis[t], t});
              }
          }
      }
  }
  int main() {
      int n, m, u, v, w;
      while (scanf("%d%d", &n, &m) && (n || m)) {
          tot = 0;
          memset(tail, -1, sizeof(tail));
          while (m--) {
              scanf("%d%d%d", &u, &v, &w);
              add(u, v, w);
              add(v, u, w);
          }
          dij();
          printf("%d
  ", dis[n]);
      }
      return 0;
  }

• 迪杰斯特拉算法堆优化--O(nlgn) 以vector建图

  #include "bits/stdc++.h"
  using namespace std;
  typedef pair<int, int> PII;
  const int MAXN = 105;
  const int INF = 0x3f3f3f3f;
  vector<PII> vc[MAXN];
  int dis[MAXN];
  bool use[MAXN];
  void dij() {
      memset(dis, INF, sizeof(dis));
      memset(use, false, sizeof(use));
      priority_queue<PII, vector<PII>, greater<PII> > que;
      for (int i = 0; i < vc[1].size(); i++) {
          PII p = vc[1][i];
          if (p.second < dis[p.first]) {
              dis[p.first] = p.second;
              que.push({dis[p.first], p.first});
          }
      }
      use[1] = true;
      while (!que.empty()) {
          int v = que.top().second;
          que.pop();
          if (use[v]) continue;
          use[v] = true;
          for (int i = 0; i < vc[v].size(); i++) {
              PII p = vc[v][i];
              if (dis[v] + p.second < dis[p.first]) {
                  dis[p.first] = dis[v] + p.second;
                  que.push({dis[p.first], p.first});
              }
          }
      }
  }
  int main() {
      int n, m, u, v, w;
      while (scanf("%d%d", &n, &m) && (n || m)) {
          for (int i = 1; i <= n; i++) vc[i].clear();
          while (m--) {
              scanf("%d%d%d", &u, &v, &w);
              vc[u].push_back({v, w});
              vc[v].push_back({u, w});
          }
          dij();
          printf("%d
  ", dis[n]);
      }
      return 0;
  }

• 弗洛伊德算法--O(n^3)

  #include"iostream"
  #include"cstring"
  #include"cstdio"
  using namespace std;
  const int inf = 0x3f3f3f3f;
  typedef long long LL;
  int map[105][105];
  int n, m;
  void Floyd() {
      for(int k = 1; k <= n; k++)
      for(int i = 1; i <= n; i++)
      for(int j = 1; j <= n; j++)
      if(map[i][k] + map[k][j] < map[i][j])
      map[i][j] = map[i][k] + map[k][j];
  }
  int main() {
      int a, b, c;
      while(scanf("%d%d", &n, &m) && (n || m)) {
          memset(map, inf, sizeof(map));
          while(m--) {
              scanf("%d%d%d", &a, &b, &c);
              if(map[a][b] > c)
              map[a][b] = map[b][a] = c;
          }
          Floyd();
          printf("%d
  ", map[1][n]);
      }
      return 0;
  }

• SPFA算法--O(KE)--E是边数，K一般为2-3

  #include"iostream"
  #include"cstring"
  #include"cstdio"
  #include"queue"
  using namespace std;
  const int inf = 0x3f3f3f3f;
  typedef long long LL;
  int map[105][105];
  int ans[105], n, m;
  bool flag[105];
  void SPFA() {
      memset(ans, inf, sizeof(ans));
      memset(flag, true, sizeof(flag));
      ans[1] = 0;
      queue<int>q;
      q.push(1); flag[1] = false;
      while(!q.empty()) {
          int v = q.front();
          flag[v] = true;
          q.pop();
          for(int i = 1; i <= n; i++)
          if(ans[v] + map[v][i] < ans[i]) {
              ans[i] = ans[v] + map[v][i];
              if(flag[i]) {
                  q.push(i);
                  flag[i] = false;
              }
          }
      }
  }
  int main() {
      int a, b, c;
      while(scanf("%d%d", &n, &m) && (n || m)) {
          memset(map, inf, sizeof(map));
          while(m--) {
              scanf("%d%d%d", &a, &b, &c);
              if(map[a][b] > c)
              map[a][b] = map[b][a] = c;
          }
          SPFA();
          printf("%d
  ", ans[n]);
      }
      return 0;
  }

• 深度优先搜索算法

  #include"iostream"
  #include"cstring"
  #include"cstdio"
  #include"queue"
  using namespace std;
  const int inf = 0x3f3f3f3f;
  typedef long long LL;
  int map[105][105];
  int ans, n, m;
  bool flag[105];
  void DFS(int i, int k) {
      if(i == n) {
          if(k < ans)
          ans = k;
          return;
      }
      for(int j = 1; j <= n; j++)
      if(flag[j] && k + map[i][j] < ans) {
          flag[j] = false;
          DFS(j, k + map[i][j]);
          flag[j] = true;
      }
  }
  int main() {
      int a, b, c;
      while(scanf("%d%d", &n, &m) && (n || m)) {
          memset(map, inf, sizeof(map));
          while(m--) {
              scanf("%d%d%d", &a, &b, &c);
              if(map[a][b] > c)
              map[a][b] = map[b][a] = c;
          }
          memset(flag, true, sizeof(flag));
          flag[1] = false;
          ans = inf; DFS(1, 0);
          printf("%d
  ", ans);
      }
      return 0;
  }