tyvj1122 noip2009 最优贸易——by rfy

来源：互联网发布：淘宝店铺如何升级天猫编辑：程序博客网时间：2024/06/06 03:12

两遍spfa即可

SB地把L打成1。。。居然还60分。。。

code：

#include<cstdio>#include<cstring>#include<vector>using namespace std;vector<int> ljb[1000000];vector<int>::iterator iv;int n,m,x[1000000],y[1000000],v[1000000],maxn[1000000],minn[1000000],flag[1000000],q[1000000],ans,i,l,r,p[1000000],pos;bool relax(int x,int y){if (minn[x]<minn[y]){minn[y]=minn[x];return 1;}else return 0;}bool relax2(int x,int y){if (maxn[x]>maxn[y]){maxn[y]=maxn[x];return 1;}else return 0;}int main(){scanf("%d%d",&n,&m);for (i=1;i<=n;i++)scanf("%d",&v[i]);for (i=1;i<=m;i++)scanf("%d%d%d",&x[i],&y[i],&p[i]);//readln;for (i=1;i<=m;i++)if (p[i]==1)    ljb[x[i]].push_back(y[i]);else ljb[x[i]].push_back(y[i]),ljb[y[i]].push_back(x[i]);for (i=1;i<=n;i++)    minn[i]=100000000;minn[1]=v[1];l=0;r=1;q[r]=1;flag[1]=1;while (l!=r){l++;pos=q[l];flag[pos]=0;for (iv=ljb[pos].begin();iv!=ljb[pos].end();iv++){if (minn[*iv]>1000000){minn[*iv]=v[*iv];r++;q[r]=*iv;flag[*iv]=1;}    if (relax(pos,*iv))        if (!flag[*iv]){r++;q[r]=*iv;flag[*iv]=1;}}}//first spfa;for (i=1;i<=n;i++)    ljb[i].clear();memset(q,0,sizeof(q));for (i=1;i<=m;i++)    if (p[i]==1)        ljb[y[i]].push_back(x[i]);    else ljb[x[i]].push_back(y[i]),ljb[y[i]].push_back(x[i]);maxn[n]=v[n];l=0;r=1;q[r]=n;flag[n]=1;while (l!=r){l++;pos=q[l];for (iv=ljb[pos].begin();iv!=ljb[pos].end();iv++){if (maxn[*iv]==0){maxn[*iv]=v[*iv];r++;q[r]=*iv;flag[*iv]=1;}    if (relax2(pos,*iv))        if (!flag[*iv]){r++;q[r]=*iv;flag[*iv]=1;}}}//second spfa;for (i=1;i<=n;i++)    if (maxn[i]-minn[i]>ans)        ans=maxn[i]-minn[i];printf("%d",ans);}

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