LCA最近公共祖先（least common ancestors）

#include"stdio.h"
#include"string.h"
#include"iostream"
#include"queue"
#define M 111111
using namespace std;
struct st
{
    int u,v,next,w;
}edge[M*2];
int rank[M],head[M],t,pre[M],use[M],dis[M];
void init()
{
    t=0;
    memset(head,-1,sizeof(head));
}
void add(int a,int b,int w)
{
    edge[t].u=a;
    edge[t].v=b;
    edge[t].w=w;
    edge[t].next=head[a];
    head[a]=t++;
}
void bfs(int s)
{
    queue<int>q;
    memset(use,0,sizeof(use));
    memset(rank,0,sizeof(rank));
    use[s]=1;
    q.push(s);
    while(!q.empty())
    {
        int u=q.front();
        q.pop();
        for(int i=head[u];i!=-1;i=edge[i].next)
        {
            int v=edge[i].v;
            if(!use[v])
            {
                use[v]=1;
                rank[v]=rank[u]+1;
                pre[v]=u;
                dis[v]=edge[i].w;
                q.push(v);
            }
        }
    }
}//用bfs对点进行分层
int targan(int a,int b)
{
    int sum=0;
    while(a!=b)
    {
        if(rank[a]>rank[b])
        {
            sum+=dis[a];
            a=pre[a];
        }
        else
        {
            sum+=dis[b];
            b=pre[b];
        }
    }
    return sum;
}//查找

/*int targan(int a,int b)
{
    if(a==b)
        return a;
    else if(rank[a]>rank[b])
        return targan(pre[a],b);
    else
        return targan(a,pre[b]);
}*/深搜写法

int main()
{
    int n,m,a,i,b,c;
    while(scanf("%d%d",&n,&m)!=-1)
    {
        init();
        while(m--)
        {
            scanf("%d%d%d",&a,&b,&c);
            add(a,b,c);
            add(b,a,c);
        }
        bfs(1);
        for(i=1;i<=n;i++)
            printf("%d ",rank[i]);
        while(scanf("%d%d",&a,&b)!=-1)
        {
            int ans=targan(a,b);
            printf("%d
",ans);
        }
    }
}