94 lines
2.0 KiB
C++
94 lines
2.0 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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#include <queue>
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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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#define MAXN 1005
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int d[MAXN];/// distance [ From S to ... ]
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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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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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d[i]=INF;
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}
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queue<int> bus;
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bus.push(StartPoint);
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d[StartPoint]=0;
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while(!bus.empty())
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{
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int c=bus.front();
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bus.pop();
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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( 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(i)
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{
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if(c) path[i]=path[c];
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bus.push(i);
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}
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}
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if(d[i]==d[c]+mp[c][i])
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{
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if(c)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<=i; j++)
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{
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if(i==j) mp[i][j]=0;
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else mp[i][j]=mp[j][i]=INF;
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}
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}
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int tu,tv,tw;
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for(int i=0; i<m; i++)
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{
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scanf("%d%d%d",&tu,&tv,&tw);
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mp[tu][tv]=tw;
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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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