mirror of
https://github.com/Kiritow/OJ-Problems-Source.git
synced 2024-03-22 13:11:29 +08:00
98 lines
2.2 KiB
C++
98 lines
2.2 KiB
C++
#include <cstdio>
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#include <cstdlib>
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#include <cstring>
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#include <algorithm>
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using namespace std;
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#define INF 0x3f3f3f3f
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/** SPFA 单源最短路径算法 不支持负环*/
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const int MAXN = 1005;
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int d[MAXN];/// distance [ From S to ... ]
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int v[MAXN];/// visit
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int q[MAXN];/// 基于数组的队列(也可用queue等...)
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int mp[MAXN][MAXN]; /// mp[i][j] i<--> j is connected.
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int n;/// n is the number of max Point .
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int path[MAXN];
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void spfa(int StartPoint) /// d[i] is the min distance from StartPoint to i ( Both >=1 )
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{
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memset(d,0x3f,sizeof(int)*(n+1));
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memset(v,0,sizeof(int)*(n+1));
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/*
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for(int i=1;i<MAXN;i++)
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d[i]=INF,v[i]=0;*/
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int cnt=0;
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q[cnt++]=StartPoint;
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v[StartPoint]=1;
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d[StartPoint]=0;
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while(cnt>0)
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{
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int c=q[--cnt];
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v[c]=0;
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for(int i=0;i<=n;i++)
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{
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/// Here : if your mp[i][j] use INF as infinite, then use mp[c][i]!=INF.
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/// Or you may use mp[i][j]!=-1 && d[i] > d[c] + mp[c][i]
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if( mp[c][i]!=INF && d[i]>d[c]+mp[c][i] )
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{
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d[i]=d[c]+mp[c][i];
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//path[i]=min(path[i],path[c]);
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if(!v[i])
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{
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if(c) path[i]=path[c];
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v[i]=1,q[cnt++]=i;
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}
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}
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if(c&&d[i]==d[c]+mp[c][i])
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{
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path[i]=min(path[i],path[c]);
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}
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}
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}
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}
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int main()
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{
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int t;
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scanf("%d",&t);
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while(t--)
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{
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int m;
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scanf("%d %d",&n,&m);
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if(!n&&!m) break;
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n=n+1;
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for(int i=0;i<=n;i++)
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{
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for(int j=0;j<=n;j++)
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{
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if(i==j) mp[i][j]=0;
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else mp[i][j]=INF;
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}
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}
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for(int i=0;i<m;i++)
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{
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int u,v,w;
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scanf("%d %d %d",&u,&v,&w);
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mp[u][v]=w;
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}
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for(int i=0; i<=n; i++)
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{
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if(mp[0][i]!=INF)path[i]=i;//Path Init
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}
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spfa(0);
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if(d[n]<INF)
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{
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if(path[n]==n)printf("0\n");
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else printf("%d\n",path[n]);
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}
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else printf("-1\n");
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}
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return 0;
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}
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