PKU 1511 Invitation Cards (SPFA + adjacent table)

The question requires the sum of the shortest distance from the origin to all vertices and the shortest distance from all vertices to the origin. When finding the shortest distance from all vertices to the origin, a technique is used to reverse the graph, calculate the shortest distance from the origin point to all other points. In this way, you can use SPFA to obtain the shortest distance from all points to the origin point.

 

In addition, there is nothing to say, pure SPFA. In addition, dijkstra, Which is optimized to VlogE, can also be used. If you are free, write another one.

 

The Code is as follows:

 

 

#include <iostream>#include <algorithm>#include <string>#include <sstream>#include <queue>using namespace std;#define MAX 1000009#define INF 1<<30struct ENode {int to, cost, next;} enode[MAX * 4];int NE = 0;int OriginHead[MAX], RevHead[MAX];int dist[MAX];void insertEdge( int from, int to, int cost ){enode[NE].cost = cost; enode[NE].to = to; enode[NE].next = OriginHead[from]; OriginHead[from] = NE++;enode[NE].cost = cost; enode[NE].to = from; enode[NE].next = RevHead[to]; RevHead[to] = NE++;}void initDist( int n ){for (int i=0; i<=n; i++) dist[i] = INF;dist[1] = 0;}int inQueue[MAX];queue<int> Q;void SPFA( int *Head ){inQueue[1] = 1;Q.push(1);while ( ! Q.empty() ){int q = Q.front();Q.pop();inQueue[q] = 0;for ( int i=Head[q]; i!=-1; i=enode[i].next ){int e = enode[i].to;if ( dist[q] + enode[i].cost < dist[e] ) {dist[e] = dist[q] + enode[i].cost;if ( !inQueue[e] ){inQueue[e] = 1;Q.push( e );}}}}}long long getTotal( int n ){long long ret = 0;for (int i=2; i<=n; i++)ret += dist[i];return ret;}int main( ){//cout << (int)(1<<30) << endl;int T;cin >> T;while( T-- ){int n, m;scanf("%d%d", &n, &m);memset( OriginHead, -1, sizeof(OriginHead) );memset( RevHead, -1, sizeof(RevHead) );NE = 0;for (int i=0; i<m; i++){int from, to, cost;scanf( "%d%d%d", &from, &to, &cost );insertEdge( from, to, cost );}initDist( n );memset( inQueue, 0, sizeof(inQueue) );SPFA( OriginHead );long long int ans = 0;ans += getTotal( n );//cout << ans << endl;initDist( n );memset( inQueue, 0, sizeof(inQueue) );SPFA( RevHead );ans += getTotal( n );cout << ans << endl;}return 0;}