HDU ACM 1142 A Walk Through the FOREST->SPFA algorithm + memory Deep Search

Analysis: Find Jimmy from the office through the Forest back home (that is, from point 1 to 2) The shortest path there are how many, in which to meet if you want to go to a to B this road, then there is a to the end of the distance from a to the end of the distance is greater than B.

Solution: SPFA algorithm + memory Deep Search

1. SPFA find the shortest path from the end point 2 to all other points

2, the memory of Dfs from 1 start to other points deep search, the final result is dp[1].

#include <iostream> #include <queue> using namespace std; int u[2000002];int v[2000002];int w[2000002];bool vis[1001];int d[1001];int first[1001];int Next[2000002];int dp[1001]  ;        void Init (int n,int m) {int i;          for (i=1;i<=n;i++) {vis[i]=false;    First[i]=-1;dp[i]=-1; } for (i=0;i<m;i++) next[i]=-1;}   int DFS (int u) {int i,sum;if (DP[U]!=-1) return dp[u];           Memory if (u==2) return 1; End Sum=0;for (I=first[u];i!=-1;i=next[i]) {if (D[u]>d[v[i]) Sum+=dfs (V[i]);}  return dp[u]=sum;}      void SPFA (int n,int s) {queue<int> q;        int i,x,y;   for (i=1;i<=n;i++) d[i]= (i==s)? 0:0x7fffffff;      Initialize yourself to yourself as 0, other to yourself equivalent to infinity Q.push (s);          while (!q.empty ()) {X=q.front ();          Q.pop ();          Vis[x]=false;              for (I=first[x];i!=-1;i=next[i]) {y=v[i];                  if (D[y]>d[x]+w[i]) {d[y]=d[x]+w[i]; If(!vis[y])                               {vis[y]=true;                  Q.push (y);        }}}}} void Read (int m) {int i,a,b;          for (i=0;i<m;i++) {scanf ("%d%d%d", &a,&b,&w[i]);                        U[i]=a;          Store forward edge, because it is an v[i]=b graph;          Next[i]=first[a];            First[a]=i;                W[i+1]=w[i];          Store reverse Edge i++;          U[i]=b;          V[i]=a;          NEXT[I]=FIRST[B];      First[b]=i;        }} int main () {int n,m;        while (scanf ("%d", &n) ==1 && N) {scanf ("%d", &m);  Init (N,M+M);        M+m is because there is no edge, each to save two Read (m+m);     SPFA (n,2);  Find the shortest way from 2 to all other points Cout<<dfs (1) <<endl;      Starting from 1 deep search, the final result} return 0; }

HDU ACM 1142 A Walk Through the FOREST->SPFA algorithm + memory Deep Search