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  • 用线段树写Dijkstar

    如题
    noip前就想用线段树优化Dijkstar
    写那啥,感觉挺好玩的
    写了个线段树优化的Dijkstar

    #include<cstdio>
    #include<cstring>
    #include<algorithm> 
    using namespace std;
    const int maxn =10007;
    const int maxm = 500007;
    const int INF = 0x7fffffff;
    int n,m;
    inline int read() {
        int x=0;
        char c=getchar();
        while(c<'0'||c>'9') 
            c=getchar();
        while(c>='0'&&c<='9') x=x*10+c-'0',c=getchar();
        return x;
    }
    struct node{
        int v,next,w;
    }edge[maxm];
    int num=0,head[maxn];
    inline void add_edge(int a,int b,int c) {
        edge[++num].v=b;edge[num].w=c;edge[num].next=head[a];head[a]=num;
    } 
    int dis[maxn],ans[maxn],s,t;
    int tree[maxn<<2],leaf;
    inline int check(int i,int j) {
        return dis[i]<dis[j]?i:j;
     } 
    inline void build() {
        std::memset(dis,0x3f,sizeof dis);// for(int i=0;i<=n+1;i++) dis[i]=INF;
        for(leaf=1;leaf<=n;leaf<<=1);--leaf;
        for(int i=1;i<=n;++i)tree[leaf+i]=i;
    }
    inline void modify(int x,int y) {
        dis[x]=y,x+=leaf,x>>=1;
        while(x) tree[x]=check(tree[x<<1],tree[x<<1|1]),x=x>>1;
    }
    void dijkstra(int s) {
        build();
        dis[s]=0;
        int u=s;
        for(int i=1;i<=n;++i) {
        	ans[u]=dis[u];
            const int disu=dis[u];
        	modify(u,INF); 
        	for(int j=head[u];j;j=edge[j].next){
          		int v=edge[j].v;
          		if(dis[v]<INF&&dis[v]>disu+edge[j].w)
            		modify(v,disu+edge[j].w);
        	}
        	u=tree[1];
      	}
    }
    inline void put(int x)
    {
        if (x > 9) put(x / 10);
        putchar(x % 10 + 48);   
    }
    
    int main() {
        int k;
        n=read(),m=read(),k=read();
        for(int a,b,c,i=1;i<=m;++i) {
            a=read(),b=read(),c=read();
            add_edge(a,b,c);
        }
        dijkstra(k);
        for(int i=1;i<=n;++i) {
        	if(dis[i]==0x3f3f3f3f)ans[i]=INF;
            put(ans[i]), putchar(' ');
        }
        return 0;
    }
    
    
    
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  • 原文地址:https://www.cnblogs.com/sssy/p/7856611.html
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