模板--最短路(简单)
2016-02-15 16:30
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以POJ 1847为例。
/* 有N个路口,计算从a路口到b路口的最短转弯数。 对于每一个路口,有t个分叉口,第一个分叉口是直行,也就是不用转弯 剩下的t-1个路口都需要转弯一次。 */ /************Dijkstra***************/ #include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <cmath> #include <queue> #include <stack> #include <vector> using namespace std; const int maxn = 110; const int maxm = 10010; const int INF = 0x3f3f3f3f; int map[maxn][maxn], n, a, b, t, p; int Dijkstra(int s, int e)//212K 47MS { int vis[maxn], dis[maxn]; memset(vis, 0, sizeof(vis)); for (int i = 1; i <= n; i++) dis[i] = map[s][i]; vis[s] = 1; for (int i = 0; i < n; i++) { int k = -1; int tmp = INF; for (int j = 1; j <= n;j++) if (!vis[j] && dis[j] < tmp) { k = j; tmp = dis[j]; } if (k == -1) break; vis[k] = 1; for (int j = 1; j <= n; j++) if (!vis[j] && map[k][j] < INF) dis[j] = min(dis[j], dis[k] + map[k][j]); } return dis[e]; } int main() { #ifdef LOCAL freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif while (~scanf("%d%d%d", &n, &a, &b)) { for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) if (i == j) map[i][j] = 0; else map[i][j] = INF; for (int i = 1; i <= n; i++) { scanf("%d", &t); for (int j = 1; j <= t; j++) { scanf("%d", &p); if (j == 1) map[i][p] = 0; else map[i][p] = 1; } } int ans = Dijkstra(a, b); if (ans == INF) ans = -1; printf("%d\n", ans); } return 0; }
/********Dijkstra+Heap*******/ #include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <cmath> #include <queue> #include <stack> #include <vector> using namespace std; const int maxn = 110; const int maxm = 10010; const int INF = 0x3f3f3f3f; struct Edge { int v, w, next; }edge[maxm]; int vis[maxn], head[maxn]; int n, a, b, t, p, tot; void AddEdge(int from, int to, int dist, int k) { edge[k].v = to; edge[k].w = dist; edge[k].next = head[from]; head[from] = k; } struct HeapNode { int dist, u; bool operator < (const HeapNode& rhs) const { return dist > rhs.dist; } }dis[maxn]; int Dijkstra_Heap(int s,int e)//184K 0MS { priority_queue<HeapNode> q; while (!q.empty()) q.pop(); for (int i = 1; i <= n; i++)//结点标号:1--n { dis[i].u = i; dis[i].dist = INF; } dis[s].dist = 0; memset(vis, 0, sizeof(vis)); q.push(dis[s]); while (!q.empty()) { HeapNode x = q.top(); q.pop(); int u = x.u; if (vis[u]) continue; vis[u] = 1; for (int i = head[u]; i != -1; i = edge[i].next) { int v = edge[i].v; int w = edge[i].w; if (dis[v].dist > dis[u].dist + w) { dis[v].dist = dis[u].dist + w; q.push(dis[v]); } } } return dis[e].dist; } int main() { #ifdef LOCAL freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif while (~scanf("%d%d%d", &n, &a, &b)) { memset(head, -1, sizeof(head)); tot = -1; for (int i = 1; i <= n; i++) { scanf("%d", &t); for (int j = 1; j <= t; j++) { tot++; scanf("%d", &p); if (j == 1) AddEdge(i, p, 0, tot); else AddEdge(i, p, 1, tot); } } int ans = Dijkstra_Heap(a, b); if (ans == INF) ans = -1; printf("%d\n", ans); } return 0; }
/**********Floyd***********/ #include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <cmath> #include <queue> #include <stack> #include <vector> using namespace std; const int maxn = 110; const int maxm = 10010; const int INF = 0x3f3f3f3f; int map[maxn][maxn], n, a, b, t, p; int floyd(int s,int e)//212K 16MS { for (int k = 1; k <= n; k++) for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) map[i][j] = min(map[i][j], map[i][k] + map[k][j]); return map[s][e]; } int main() { #ifdef LOCAL freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif while (~scanf("%d%d%d", &n, &a, &b)) { for (int i = 1; i <= n; i++) for (int j = 1; j <= n; j++) if (i == j) map[i][j] = 0; else map[i][j] = INF; for (int i = 1; i <= n; i++) { scanf("%d", &t); for (int j = 1; j <= t; j++) { scanf("%d", &p); if (j == 1) map[i][p] = 0; else map[i][p] = 1; } } int ans=floyd(a,b); if (ans == INF) ans = -1; printf("%d\n", ans); } return 0; }
/**************Bellman_Ford*********************/ #include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <cmath> #include <queue> #include <stack> #include <vector> using namespace std; const int maxn = 110; const int maxm = 10010; const int INF = 0x3f3f3f3f; int n, a, b, uu, vv, ww, t, tot, p; int dis[maxn]; struct Edge { int u, v, w; }edge[maxm]; int Bellman_Ford(int s, int e)//172K 0MS { for (int i = 1; i <= n; i++) { if (i == s) dis[i] = 0; else dis[i] = INF; } for (int i = 0; i < n - 1; i++) for (int j = 0; j <= tot; j++) { int x = edge[j].u; int y = edge[j].v; int z = edge[j].w; dis[y] = min(dis[y], dis[x] + z); } return dis[e]; } int main() { #ifdef LOCAL freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif while (~scanf("%d%d%d", &n, &a, &b)) { tot = -1; for (int i = 1; i <= n; i++) { scanf("%d", &t); for (int j = 1; j <= t; j++) { ++tot; scanf("%d", &p); edge[tot].u = i; edge[tot].v = p; if (j == 1) edge[tot].w = 0; else edge[tot].w = 1; } } int ans = Bellman_Ford(a, b); if (ans == INF) ans = -1; printf("%d\n", ans); } return 0; }
/***********SPFA+QUEUE***********/ /***********SPFA+STACK***********/ #include <iostream> #include <cstdio> #include <cstring> #include <algorithm> #include <cmath> #include <queue> #include <stack> #include <vector> using namespace std; const int maxn = 110; const int maxm = 10010; const int INF = 0x3f3f3f3f; int dis[maxn], head[maxn], vis[maxn]; int n, a, b, t, p, tot; struct Edge { int v, w, next; }edge[maxm]; void AddEdge(int u, int v, int w, int k) { edge[k].v = v; edge[k].w = w; edge[k].next = head[u]; head[u] = k; } int SPFA_QUEUE(int s, int e)//队列实现 184K 16MS { queue<int> q; if (!q.empty()) q.pop(); for (int i = 1; i <= n; i++) { if (i == s) dis[i] = 0; else dis[i] = INF; } memset(vis, 0, sizeof(vis)); vis[s] = 1; q.push(s); while (!q.empty()) { int uu = q.front(); q.pop(); vis[uu] = 0; for (int i = head[uu]; i != -1; i = edge[i].next) { int vv = edge[i].v; int ww = edge[i].w; if (dis[uu] < INF && dis[vv] > dis[uu] + ww) { dis[vv] = dis[uu] + ww; if (!vis[vv]) { vis[vv] = 1; q.push(vv); } } } } return dis[e]; } int SPFA_STACK(int s, int e)//栈实现 184K 0MS { stack<int> q; if (!q.empty()) q.pop(); for (int i = 1; i <= n; i++) { if (i == s) dis[i] = 0; else dis[i] = INF; } memset(vis, 0, sizeof(vis)); vis[s] = 1; q.push(s); while (!q.empty()) { int uu = q.top(); q.pop(); vis[uu] = 0; for (int i = head[uu]; i != -1; i = edge[i].next) { int vv = edge[i].v; int ww = edge[i].w; if (dis[uu] < INF && dis[vv] > dis[uu] + ww) { dis[vv] = dis[uu] + ww; if (!vis[vv]) { vis[vv] = 1; q.push(vv); } } } } return dis[e]; } int main() { #ifdef LOCAL freopen("in.txt", "r", stdin); //freopen("out.txt", "w", stdout); #endif while (~scanf("%d%d%d", &n, &a, &b)) { tot = -1; memset(head, -1, sizeof(head)); for (int i = 1; i <= n; i++) { scanf("%d", &t); for (int j = 1; j <= t; j++) { ++tot; scanf("%d", &p); if (j == 1) AddEdge(i, p, 0, tot); else AddEdge(i, p, 1, tot); } } //int ans = SPFA_QUEUE(a, b); int ans = SPFA_STACK(a, b); if (ans == INF) ans = -1; printf("%d\n", ans); } return 0; }
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