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
反正现在退役了也是闲的，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;
}