No.11 - POJ3268 SPFA 最短路

SPFA算法，求两次最短路：

// ShellDawn
// POJ3268
// No.11

#include<algorithm>
#include<cstdio>
#include<iostream>
#include<cstring>
#include<queue>
#include<vector>
#define MM(x) memset(x,0,sizeof(x))
#define MMF(x) memset(x,0x3f,sizeof(x))
#define INF 0x3f3f3f3f
#define NINF 0xc0c0c0c0
using namespace std;


#define maxn 1005
int n,m,s;
// 邻接表
int EA[maxn][maxn][2];
int cntA[maxn];
int EB[maxn][maxn][2];
int cntB[maxn];
// end
int ansA[maxn];
int ansB[maxn];

void SPFA(int ans[maxn],int E[maxn][maxn][2],int cnt[maxn]){
    queue<int> q;
    ans[s] = 0;
    q.push(s);
    while(!q.empty()){
        int loc = q.front();
        q.pop();
        for(int i=0;i<cnt[loc];i++){
            int next = E[loc][i][0];
            int v = E[loc][i][1];
            if(ans[loc] + v < ans[next]){
                ans[next] = ans[loc] + v;
                q.push(next);
            }
        }
    }
}

int main(){
    //freopen("A.txt","r",stdin);
    while(~scanf("%d%d%d",&n,&m,&s)){
        MM(EA);MM(EB);MM(cntA);MM(cntB);
        for(int i=0;i<m;i++){
            int a,b,c;
            cin>>a>>b>>c;
            int loc = cntA[a];
            EA[a][loc][0] = b;
            EA[a][loc][1] = c;
            cntA[a] ++;
            loc = cntB[b];
            EB[b][loc][0] = a;
            EB[b][loc][1] = c;
            cntB[b] ++;
        }
        MMF(ansA);
        SPFA(ansA,EA,cntA);
        MMF(ansB);
        SPFA(ansB,EB,cntB);
        int ans = 0;
        for(int i=1;i<=n;i++){
            if(i==s) continue;
            ans = max(ans,ansA[i] + ansB[i]);
        }
        cout<<ans<<endl;
    }
    return 0;
}