DIjkstra (reverse side) POJ 3268 Silver Cow Party | | POJ 1511 Invitation Cards

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Test instructions: The map, all points go to the X-point, at the point of return from X, ask the largest one of the shortest distance

Analysis: Run the most short-circuit on the pros and cons of the graph, open two arrays to record the distance from X to the rest of the points, so that you can find the shortest possible short circuit and back.

POJ 3268

#include <bits/stdc++.h> #include <cstdio> #include <queue> #include <algorithm> #include <cstring>using namespace Std;typedef long long ll;const int N = 1e6 + 5;const int E = n;const int INF = 0x3f3f3f3f;s Truct edge{int u, V, W, NEX; Edge () {}edge (int u, int v, int w, int nex): U (U), V (v), W (W), NEX (NEX) {}bool operator < (const Edge &AMP;R) const {return w > R.W;}} Edge[2][e];int head[n];int d[2][n];bool vis[n];int N, M, x, E;inline int read (void) {int f = 1, ret = 0;char ch = getchar ( ); while (Ch > ' 9 ' | | ch < ' 0 ') {if (ch = = '-') F = -1;ch = GetChar ();} while (Ch <= ' 9 ' && ch >= ' 0 ') {ret = RET * + CH-' 0 '; ch = GetChar ();} return ret * f;} void init (void) {memset (head,-1, sizeof (head)); e = 0;} void Add_edge (int u, int v, int w) {Edge[0][e] = Edge (U, V, W, Head[u]); Head[u] = e++;} void Build_re_graph (void) {memset (head,-1, sizeof (head)), E = 0;for (int i=0; i<m; ++i) {edge[1][e] = Edge (Edge[0][i]. V, EDGE[0][I].U, EDGE[0][I].W, HEAD[EDGE[0][I].V]); HEAD[EDGE[0][I].V] = e++;}} void SPFA (int s, int tp) {memset (D[TP], INF, sizeof (D[TP])), memset (Vis, false, sizeof (VIS));d [tp][s] = 0;vis[s] = true;  Queue<int> Que;que.push (s); while (!que.empty ()) {int u = que.front (); Que.pop (); Vis[u] = false;for (int i=head[u]; ~i; I=edge[tp][i].nex) {int v = edge[tp][i].v, W = edge[tp][i].w;if (D[tp][v] > D[tp][u] + W) {D[tp][v] = D[tp][u] + w;if (!v Is[v]) {Vis[v] = True;que.push (v);}}}} void Dijkstra (int s, int tp) {memset (Vis, false, sizeof (VIS)), memset (D[TP], INF, sizeof (D[TP]));d [Tp][s] = 0;priority_q Ueue<edge> Que;que.push (Edge (0, S, D[tp][s], 0)), while (!que.empty ()) {int u = que.top (). V;que.pop (); if (Vis[u]) continue;for (int i=head[u]; ~i; i=edge[tp][i].nex) {int v = edge[tp][i].v, W = edge[tp][i].w;if (!vis[v] && d[tp][ V] > D[tp][u] + W) {D[tp][v] = D[tp][u] + w;que.push (Edge (0, V, D[tp][v], 0));}}} int Get_max (void) {int ret = 0;for (int i=1; i<=n; ++i) {ret = max (ret, d[0][i] + d[1][I]);} return ret;} int main (void) {while (scanf ("%d%d%d", &n, &m, &x) = = 3) {init (); for (int u, V, W, i=0; i<m; ++i) {scanf ("% D%d%d ", &u, &v, &w); Add_edge (U, V, W);} SPFA (x, 0);D Ijkstra (x, 0); Build_re_graph ()//SPFA (x, 1);D Ijkstra (x, 1); int ans = Get_max ();p rintf ("%d\n", ans);} return 0;}

There is a similar problem, is to seek the most and, in fact, are the same

POJ 1511

#include <bits/stdc++.h> #include <cstdio> #include <queue> #include <algorithm> #include <cstring>using namespace Std;typedef long long ll;const int N = 1e6 + 5;const int E = n;const int INF = 0x3f3f3f3f;s Truct edge{int u, V, W, NEX; Edge () {}edge (int u, int v, int w, int nex): U (U), V (v), W (W), NEX (NEX) {}bool operator < (const Edge &AMP;R) const {return w > R.W;}} Edge[2][e];int head[n];int d[n];bool vis[n];int N, M, e;inline int read (void) {int f = 1, ret = 0;char ch = getchar (); whil E (ch > ' 9 ' | | ch < ' 0 ') {if (ch = = '-') F = -1;ch = GetChar ();} while (Ch <= ' 9 ' && ch >= ' 0 ') {ret = RET * + CH-' 0 '; ch = GetChar ();} return ret * f;} void init (void) {memset (head,-1, sizeof (head)); e = 0;} void Add_edge (int u, int v, int w) {Edge[0][e] = Edge (U, V, W, Head[u]); Head[u] = e++;} void Build_re_graph (void) {memset (head,-1, sizeof (head)), E = 0;for (int i=0; i<m; ++i) {edge[1][e] = Edge (Edge[0][i]. V, edge[0][i].u, EDGE[0][I].W, head[EDGE[0][I].V]); HEAD[EDGE[0][I].V] = e++;}} void SPFA (int s, int tp) {memset (d, INF, sizeof (d)), memset (Vis, false, sizeof (VIS));d [s] = 0;vis[s] = True;queue<int > Que;que.push (s), while (!que.empty ()) {int u = que.front (); Que.pop (); Vis[u] = false;for (int i=head[u]; ~i; i=edge[ Tp][i].nex) {int v = edge[tp][i].v, W = edge[tp][i].w;if (D[v] > D[u] + W) {D[v] = D[u] + w;if (!vis[v]) {Vis[v] = True;qu E.push (v);}}}} ll get_sum (void) {LL ret = 0;for (int i=1; i<=n; ++i) {ret + = D[i];} return ret;} int main (void) {int t;scanf ("%d", &t), while (t--) {scanf ("%d%d", &n, &m), Init (); for (int u, V, W, i=0; i<m ; ++i) {//scanf ("%d%d%d", &u, &v, &w); u = Read (); v = Read (); w = read (); Add_edge (U, V, W);} SPFA (1, 0); ll ans = get_sum (); Build_re_graph (); SPFA (1, 1), ans + = get_sum ();p rintf ("%lld\n", ans); return 0;}

　　

DIjkstra (reverse side) POJ 3268 Silver Cow Party | | POJ 1511 Invitation Cards