#include<stdio.h>
#include<stdlib.h>
#define MAX 1002
int join[MAX][MAX],cont[MAX],used[MAX],win[MAX];
int np,mark,fri;
int tree(int aa)
{
    int i,j,k,mar=0,min1=MAX,min2=MAX;
    used[aa]=1;
    if(cont[aa]==1&&aa!=fri)//!!cout为1可为终点，亦可为起点~！！
    {
       win[aa]=aa;
        return 0;
    }
    for(i=1;i<=np;i++)
    {
        if(join[aa][i]&&!used[i])
        {

            k=tree(i);
            if(!k&&min1>win[i])
            {
                mar=1;
                min1=win[i];
            }
            if(k&&min2>win[i])
                min2=win[i];
        }
    }
    if(mar)
    {
        win[aa]=min1;
            return 1;
    }
    else
    {
        win[aa]=min2;
        return 0;
    }
}

int main()
{
    int i,j,k,mar=0;
    scanf("%d%d",&np,&fri);
    for(i=1;i<np;i++)
    {
        scanf("%d%d",&j,&k);
        join[j][k]=1;
        join[k][j]=1;
        cont[j]++;
        cont[k]++;
    }
    k=tree(fri);
    if(k)printf("First player wins flying to airport %d\n",win[fri]);
    else printf("First player loses\n");
//    system("pause");
    return 0;
}

I find where I made the mistake,
I just misunderstand the porblem...